-Top speed: 20 km/h (for light cavalry)

-Top speed: 20 km/h (for light cavalry charges)

Edit:

It was pointed out a horse top speed is actually 90 Km/h and not 20 Km/h as I initially claimed. That number was from wikipedia and corresponds to their maximum charging speeds, it's only this high since: "moving faster resulted in a break in formation and fatigued horses".

That means that light cavarly could probably outrun the bulls chasing them, at least for certain distances. One of the sources claims bulls can maintain this speed for up to 400m, other sources spoke about horses doing faster sprints for only about 200m. So maybe the bulls still have a chance as anti light cavalry units, albeit with a shorter oportunity window.

Additionally, bulls top speed wasn't measured for a mounted bull, or one wearing armor (for obvious reasons), so that's an obvious difference from the horses, that tips the numbers in favor of the bulls. Still, I take this liberty from the bull's lack of selective breeding for combat, and the fact that the weight differences means a rider and armor woulnd't be such a heavy toll for bulls, comparatively.

In your setting you mention having elves wha are poficient on training animals, I assume they would also be good at selectively breeding them to produce certain traits. All examples of bulls' characteristics we see nowadays aren't a result of optimization for war. Therefore it's very reasonable for your bulls to outperform out modern counterparts in a few desirable measures.

-Marching pace: 40 km/day (with weightloss) 15 km/day (comfortably)

Bare in mind heavy warhorses were meant for carrying artillery and other supplies and it isn't confrimed they wether actually carried knigts into battle in the middle ages. The horses that would be used for this would be the medium ones. Why is this relevant, because a horse can carry 20-30% of its weight on top of it. A suit of armor could weight betwheen 20-25 Kg in the middle ages, with horse armor being an additional 23 Kg.

An additional mention about marching pace, knights wuldn't ride their warhorses for everyday marches, they would reserve those for battle.

Okay, so what do we have here. We have a stronger beast, capable of faster charges, while also being heavyer so harder to stop and capable of more damage. Cavalry charges were partly used to cause soldiers to scatter and flee, a wall of bulls running towards you at 40 Km/h can be more effective at it that a wall of horses running at 20 Km/h. Also, bulls would carry more momentum, could be more heaviliy armored, thanks to their extra weight and could use their horns to deflect spears somewhat (especially if your elves are good at training them to do this, plus there can be horns attatchments added to make this easier).

Are they disadvantages? Sure, there's less endurance and maneuverability. Those are pretty relavant factors, I'll give you that. Some of this may be overcome with breeding though. Their deficit in maneubrability can be made up with tactics, perhaps your bulls can't retreat as fast. Okay, but maybe they don't need to, or not as quickly, since they are capable of more effective charges and could create more chaos on the enemies frontlines.

In addition, the heavier bulls could even carry two armored knights on top. Is this a viable strategy? I don't know. Maybe the one in the back is facing backwards, to defend the rearguard while the bull turns around. Maybe they unmount when the charge looses momentum creating a stronger front, while the foot army catches up. Maybe elves are nimble enough and well coordinated to make this fighting style work.

As for the other issues raised. I don't see corpses getting stuck in the horns as such a big issue. I mean it's not clear to me goring would be all that common, much less goring and then the body remaining there. If this were an issue, the animal could be trained to try to remove the body tilting its head downwards. Worst case scenario you cover the horns so they are more bludgeoning than piercing weapons, a hit would still mess you up, but bodies worl no loger get stuck there.

As to bulls being worse at scouting and other cavalry jobs that focus on sustained speed and maneuverability, sure, I can agree to that. But those jobs weren't fullfilled by medium and heavy cavalry. That's the role the bulls play. I'd wager bulls wouldn't be great at archery or siege defense either, but that's not how you approach warfare viability. They don't need to be good a everything, just good at something that you can use.

Another job the bull would be better at: counter cavalry shock tactics. Say you need to transport goods to your army (and this is of special importance to you cause bulls eat more). Your enemy has nimble cavalry that harasses your resource lines. Normal heavy cavalry isn't effective against them cause you lose on speed ot them. Pikemen could be useful but not if they shoot arrows at you and leave without engaging. So waht you use to defend your caravans are more bull cavalry. Why? Cause same as the normal heavy cavalry, your knights will be more heavily armored so if they get into melee range is game over for the light cavalry, but the key difference is you bulls can actually cath up to them. Sure thay can't keep up with a long chase, but if the attackers get into charge range, good luck. So this way, even if you don't have light cavalry (aside from scouting perhaps), you can still deny some of their advantages for your enemy.

In your setting you mention having elves who are proficient on training animals, I assume they would also be good at selectively breeding them to produce certain traits. All examples of bulls' characteristics we see nowadays aren't a result of optimization for war. Therefore it's very reasonable for your bulls to outperform out modern counterparts in a few desirable measures.

-Marching pace: 40 km/day (weightless) 15 km/day (comfortably)

Bare in mind heavy warhorses were meant for carrying artillery and other supplies and it isn't confirmed they whether actually carried knights into battle in the middle ages. The horses that would be used for this would be the medium ones. Why is this relevant, because a horse can carry 20-30% of its weight on top of it. A suit of armor could weight between 20-25 Kg in the middle ages, with horse armor being an additional 23 Kg.

An additional mention about marching pace, knights wouldn't ride their warhorses for everyday marches, they would reserve those for battle.

Okay, so what do we have here. We have a stronger beast, capable of faster charges, while also being heavier so harder to stop and capable of more damage. Cavalry charges were partly used to cause soldiers to scatter and flee, a wall of bulls running towards you at 40 Km/h can be more effective at it that a wall of horses running at 20 Km/h. Also, bulls would carry more momentum, could be more heavily armored, thanks to their extra weight and could use their horns to deflect spears somewhat (especially if your elves are good at training them to do this, plus there can be horns attachments added to make this easier).

Are they disadvantages? Sure, there's less endurance and maneuverability. Those are pretty relevant factors, I'll give you that. Some of this may be overcome with breeding though. Their deficit in maneuverability can be made up with tactics, perhaps your bulls can't retreat as fast. Okay, but maybe they don't need to, or not as quickly, since they are capable of more effective charges and could create more chaos on the enemies front lines.

In addition, the heavier bulls could even carry two armored knights on top. Is this a viable strategy? I don't know. Maybe the one in the back is facing backwards, to defend the rearguard while the bull turns around. Maybe they unmounted when the charge looses momentum creating a stronger front, while the foot army catches up. Maybe elves are nimble enough and well coordinated to make this fighting style work.

As for the other issues raised. I don't see corpses getting stuck in the horns as such a big issue. I mean it's not clear to me goring would be all that common, much less goring and then the body remaining there. If this were an issue, the animal could be trained to try to remove the body tilting its head downwards. Worst case scenario you cover the horns so they are more bludgeoning than piercing weapons, a hit would still mess you up, but bodies would no longer get stuck there.

As to bulls being worse at scouting and other cavalry jobs that focus on sustained speed and maneuverability, sure, I can agree to that. But those jobs weren't fulfilled by medium and heavy cavalry. That's the role the bulls play. I'd wager bulls wouldn't be great at archery or siege defense either, but that's not how you approach warfare viability. They don't need to be good a everything, just good at something that you can use.

Another job the bull would be better at: counter cavalry shock tactics. Say you need to transport goods to your army (and this is of special importance to you cause bulls eat more). Your enemy has nimble cavalry that harasses your resource lines. Normal heavy cavalry isn't effective against them cause you lose on speed ot them. Pike-men could be useful but not if they shoot arrows at you and leave without engaging. So what you use to defend your caravans are more bull cavalry. Why? Cause same as the normal heavy cavalry, your knights will be more heavily armored so if they get into melee range is game over for the light cavalry, but the key difference is you bulls can actually catch up to them. Sure they can't keep up with a long chase, but if the attackers get into charge range, good luck. So this way, even if you don't have light cavalry (aside from scouting perhaps), you can still deny some of their advantages for your enemy.