Which is More Positively Effective, Math-Wise: Modifier Bonuses, or Expertise?

Question

After my previous question about my character, I went off the deep end to find what role is needed in my party, exactly. Long-story short, we need a high DEX skill monkey. I'll have trouble with the first part, but the second was immediately doable, since Bards are good skill monkeys. After some research, however, I found a comment on rpgbot.net, which I hold to be a reasonably trustworthy opinion on DnD, that says,

At high levels we’ll have bonuses to checks that will make proficiencies feel silly.

The context of the comment is in a post optimizing a build around stacking skill and save modifiers using spells like Guidance, racial traits like Built for Success from the Autognome, and class features like the Peace Domain Cleric's Emboldening Bond.

That raised the question in my mind, "What's the point of pursuing proficiency and expertise when I could just stack modifier bonuses?"

So, the question at hand is this: Is stacking a lot of skill/save bonuses more effective than proficiency or expertise in those same skills/saves?

Answer 1

Stacking wins by numbers, but you can do both

My main recommendation is to not focus to myopically on maximizing skill rolls. You also can mix-and-match and benefit from both expertise and stacking bonuses as relatively little cost, so you may not need to make an either-or choice on it.

What is numerically better?

As an optimization question for maximizing bonuses to a any given skill roll, this comes down to how you can build a character that has abilities to grant bonuses, and what the expected contribution of those is. You can then compare this vs the character development investment needed to pick up more skills for the flat bonus from having Expertise in the skill. I'll assume as you are talking about the build of your character for this, no help from others for the comparison. Here are a few stackable bonuses, along with some sources to get them. This is focused on skill bonuses, not saves, as you say you are looking to build a skill monkey:

• Fortune of the Many: +3 (number of allies) from Hobgolin race; usable proficiency bonus times per long rest

• Guidance cantrip: +1d4 (2.5) - Cleric 1, or spell feats that give cantrips like Magic Initiate

• Emboldening Bond: +d4 (2.5) to a save/check - Peace Domain cleric 1, limited to proficiency bonus times per long rest

• Dark One's Own Luck: +d10 (5.5) to save/check - Fiend warlock 6, once per short rest

• Flash of Genius: + Int mod, if optimized +4 to +5 (outside of Tome shenanigans) - Artificer 7, limited to Int mod times per long rest

I left off Bardic Inspiration, as that does not work on yourself, only on others, and magic items, as these would help both build approaches.

You can pick up every permanent skill by level 7, if you optimize for that, 6 of them with expertise, with a bonus of +3 or +6. From first level, the ability stacking approach with a Hobgoblin Peace Domain cleric 1 would already give you +8, so going for skills just based on the numbers is not worthwhile.

Also in the endgame by level 14, with a Hobgoblin Peace Domain Cleric 1/Warlock 6/Artificer 7 you would end up with +3 + 2.5 + 2.5 + 5.5 + 5 = +18.5 total bonus. The total bonus from Expertise at level 14 is +10. So, numerically stacking bonuses will get the higher number by far, just as RPGbot claims, and it would not be a worthwile strategy trying to maximize picking up as many skills as possible. (And that is before considering bonuses may work for tool proficiencies and saves, too).

In practice

In practice, I think getting the highest bonus on all skills with stacking is not worthwhile to pursue too narrowly. Proficiency or expertise may work out better in several ways, even if the numerical bonus is smaller:

• First, many of these bonus-stacking shenanigans are limited to a number of times per day. If you need lots of investigation checks and perception checks, and sneak around with stealth checks, you will run out of applications for stacking other than guidance. Expertise does not have that problem, it is an unlimited resource.

• Second, there are situations where it would be awkward to stack these bonuses. For example in social encounters - you are at a noble's reception and want to impress your opposite number with your witty banter. Are you going to cast a spell (which is perceptible) in front of them asking your deity for guidance in your next quip?

• Third, casting a spell like guidance has an action cost. If you need to use your skill in combat, that is going to be an issue. Expertise does not have that downside.

On the other hand, being able to add bonuses may be more useful than expertise, too. Many checks do require all in the party to succeed, or at least have a successful party check. You all need to climb up that wall. You all need to sneak by the guard. You all need to swim savely to the shore. In such situations, having a single "skill moneky" character will not suffice, and helping out the weaker characters is of value.

Why choose?

Note however that the cleric which contributes a big part to stacking only needs a single level of investment. So there is no need to choose one or the other - you can have both. You have unused levels, and throwing in a level of cleric with one or three of bard, and a level of rogue is entirely feasible. Because what is better than bounded-accuracy breaking expertise or bounded-accuracy breaking bonus stacking from power-creep subclasses and races? Bounded-accuracy breaking expertise and bounded-accuracy breaking bonus stacking from power-creep subclasses and races -- at least if that is your kind of thing.

From your earlier posts, your character is already set as a Bard, and your race is already set, too. The cheapest option, if you don't care for Bard spell progression and if your DM has not banned it like many have, may be to pick up a single level in the broken Peace Domain cleric, and get a boost of +2.5 to +5 on all your checks, which is going to be as good as expertise. You really don't need higher levels in that class for skill boosting. You still can continue to level 3 bard for the expertise (and if you pick lore, 3 more skills).

Depending what you like you could then get 6 levels in warlock or 7 in artificer, although I think that as a full caster it is often better to stick with your main class as much as you can, to get access to higher level spells.

Answer 2

Expertise beats all but the most specific cheesy combos over time. Yes, the Peace Domain + Guidance (out of combat) gives you bonuses similar to what proficiency gives at mid-high levels (or turns proficiency into something similar to Expertise). But by the time you're reaching +4 proficiency bonus (+8 with Expertise), any such "always available" bonuses tend to be supplementary, the Expertise is the dominant factor.

But the skill monkey is still important for reliability when the checks get hard. First off, the problem with some checks, like Stealth or Sleight of Hand, is that you really don't want to fail them out of combat (cause now you're caught), and if you need them in combat (to Hide, snatch the MacGuffin off your enemy), it's even more critical, and your party cleric/Bard isn't going to be all that thrilled to blow their action on Guidance mid-combat. Expertise is always there for you.

Secondly, the number of available sources of effectively unlimited use stacking bonuses, even with the power creep in Tasha's/Spelljammer, is just not that high. And not every wants to play the Autognome Peace Cleric/Sorcerer(to Quicken Guidance)/Artificer(for Flash of Insight)/Bard(for Bardic Inspiration), just to make you better at the job you chose to be bad at. Even if they do like that, many of those resources will run out if you're constantly making Perception/Investigation/Sleight of Hand/Thieves' Tools/Stealth checks in a dungeon.

Beyond that, if you have Expertise, these bonuses just help more. I've played an Arcane Trickster with Gloves of Thievery (+5 to Thieves' Tools and Sleight of Hand checks) and a Cloak of Elvenkind (Advantage on Stealth rolls, enemies take Disadvantage on Perception checks). Until I got those items, even with Expertise in all those skills, I got bad luck, a lot, because dice always fail you when you need 'em (I literally never succeeded at lock picking on half a dozen attempts, despite a +7-+9 to my roll at level 3/4). The proficiency bonus increasing, my Dex getting boosted, and acquiring those magic items together is what made me reliable (having a +16 to Thieves' Tools and +11 with effectively double-advantage for Stealth makes a difference). Sure, a Peace Cleric would make it easier. They're kind of broken. But that doesn't mean I'd have done amazing by just dropping my Expertise in favor of relying on that sort of assistance.