Which of these versions of Witch Bolt is more balanced against other 1st level spells?

Question

I'm of the opinion that Witch Bolt kinda sucks. A hot take, to be sure. So I have two possible alternate versions. Which one is better at

1. Actually being a spell someone would want to take and use
2. While still being in line with other 1st level combat-type spells on the sorcerer/wizard/warlock list

Witch Bolt v2r1:
1st level evocation
Casting time: 1 action
Components: VSM (a twig from a tree that has been struck by lightning)
Range: 30ft
Duration: Concentration, up to 1 minute

A beam of crackling, blue energy lances out towards a creature within range, forming a sustained arc of lightning between you and the target. Make a ranged spell attack against that creature. On a hit, the target takes 1d12 lightning damage, and on each of your turns for the duration, you can use your bonus action to deal 2d6 lightning damage to the target automatically. The spell ends if the target has total cover from you at the end of your turn or if the target is further away than 120 ft at the end of your turn.

At higher levels. When you cast this spell using a spell slot of 2nd level or higher, the initial damage increases by 1d12 and the additional damage increases by 1d6 for each slot level above 1st.

Intent: This is a "fix the numbers and make it a bit more flexible" version. No changes other than being a bonus action to re-up the damage, giving scaling re-up'd damage, and relaxing the "the spell ends if" conditions.

Witch Bolt v2r2:
1st level evocation
Casting time: 1 action
Components: VSM (a twig from a tree that has been struck by lightning)
Range: 30ft
Duration: Concentration, up to 1 minute

A beam of crackling, blue energy lances out towards a creature within range, forming a sustained arc of lightning between you and the target. Make a ranged spell attack against that creature. On a hit, the target takes 1d12 lightning damage, and on each of your turns for the duration, you can use your bonus action to deal 1d6 lightning damage to the target automatically. The target must make a Constitution saving throw each time it takes damage from this spell. On a failed save, the target’s speed is reduced to zero until the end of its next turn. On a success, the target’s speed is reduced by 10 ft until the end of its next turn. The spell ends if the target is ever outside the spell’s range or if it has total cover from you.

At higher levels. When you cast this spell using a spell slot of 2nd level or higher, the initial damage increases by 1d12 and the additional damage increases by 1d6 for each slot level above 1st.

Intent: This one drops the additional damage, but makes it a bonus action to re-up, while adding a movement debuff. Potential issue with multiple rolls. Goal here is less of "dealing damage" but adding in a control option.

Answer 1

Both succeed at #1 and fail at #2

Both would be very strong for a first level damage spell.

Witch Bolt sucks because it takes your action every turn. At the early levels in the game, you do not have that many useful options for using bonus actions proactively. Changing this to a bonus action in both cases essentially makes it free to use the extra damage. (The first reliable alternative I can think of is Spiritual Weapon on spell level 2, which is at least at my table a much used spell, but most classes with Witch Bolt would not have that on their list).

If unopposed, on a failed save, this will deal up to 70 (or over 40 in version 2) expected damage over the duration. Even in a normal fight that only takes 4 rounds, it will deal 27 (or 16) damage. (The game aims for fights to end in 3-4 rounds, although in my own experience, many fights go longer, which is supported by empirical data in this answer, which indicates the average combat takes 5 rounds).

Compare this to other first level damage spells and how much they deal: Inflict Wounds with 11 expected damage, Magic Missile or Chromatic Orb with 10. No existing single target ones can deal that much to a creature.

(Area spells like Burning Hands with 12 expected damage, Arms of Hadar with 11 can get more damage with multiple targets, but that is situational; which bolt works reliably, no need for several targets close-by. Moreover, it can be cast at distance, which may be a plus for classes like wizards that often are not strong in melee).

There are two balancing factors: one, the spell consumes your concentration, which is a very real opportunity cost. Two, it delivers its damage only over time, instead of up-front; a point now is worth more than a point in the future. Both lessen the impact of the higher damage output, but quantifying this systematically is very difficult.

Which of the two is worse is hard to say as it is circumstantial. If you catch a strong melee opponent like an Ogre with version 2, pinning them down even for a round outside of melee range may be better than 1d6 more damage. For a kobold either might kill them dead so it won't matter. I think as the damage on both is broken already, version two which gives you more tactical options might be even stronger.

For the title of your question, I think it might be number one for this reason, but I think both are not balanced at one and a half to seven times the damage yield of other level one options. As these aspects, as well as the impact of concentration are hard to gauge, if you really want to know how players react and how good it is in practice, test the version you prefer in game.

Answer 2

Both have issues

Witch bolt is a considered a "trap" because it uses your whole action every round to sustain. Whereas a lot of other spells that sustain are either a Bonus Action, or you can pick and choose whether to "use" the spell or not (such as compelled duel and dragon's breath).

At 1st level, (and usually for a number of levels after) there are not a lot of actions a player can do repeatedly as a Bonus Action, so by changing it to a BA you free up a lot of resources that the caster can do on their action; more spells, Helping another party member, watching through your familiar's eyes (which we'll get to in a moment), stabilizing a comrade, etc. So that one switch makes both of these options much more powerful--for a 1st level spell.

R1

I see a problem, in that, the target needs total cover, or be out of range, "at the end of your turn". Meaning, they can run and hide, but it doesn't make a difference if you do something on your turn to find the target again. So they move, but you just move to see them again and it didn't matter. All you need is to reduce their cover to 3/4 and the spell keeps going. And because the spell is now a Bonus Action, you can use the Dash action to make up a lot of lost ground each turn to make sure you can see the target while keeping yourself safe. You know what else you can use your Action for? Seeing through your familiar's senses. So you can position your familiar (especially ones that have flight) in such a way that they can always find the target and prevent them from ever having "total cover".

R2

A little too powerful with the movement reduction. Pinning a creature in place makes it very easy for the rest of your party to gang up on your target. Also, you are removing the only methods to stop the damage (short of breaking your concentration); they can no longer move out of spell range and will find it near impossible to gain "total cover" once movement is impossible (without someone else carrying them away, or creating some box to hide them in).

By moving the continuation of the spell to a BA, but at only half damage (1d6 instead of 1d12), I see this as a good compromise.