So my first draft of spreadsheeting the monk was lacking in a few areas. I've updated it, and will give an explanation of how I modeled the subclass features for clarity (and correction, if appropriate).
Here's a general comparison of some monk builds:
Discipline Points: I set a reserve pool of DP that are intended for use with damage-dealing features. Other DP is left to be spent on Step of the Wind, or Stunning Strike, or whatever. The default I've set is 67% of the total DP amount.
The number of rounds available to spend DP in is defaulted to 6 — 2 fights of 3 rounds each, per short rest. Changing this only has a small effect on the graph, generally just moving lines up and down a little bit, so I'm not too worried about it.
Flurry of Blows: Since there are a number of things monk can do with its bonus action, I put a limit on the number of Flurry of Blows you can use per short rest. This limit defaults to 75% (so 4.5 rounds out of 6). This is on top of the limit on the number of DP you can spend per short rest. As you go up in level, you can use FoB more often because you have more DP, until you reach the limit of the action economy.
Warrior of Mercy
Hand of Harm: This is basically the same damage as FoB, except using Mnd as a bonus rather than Dex. Because of that, and the variations in when you might want to use each, I decided to treat FoB and HoH as fungible (can be swapped out for each other for the same gain). The limit on how often you can use them still starts off with your DP pool, so the calculations only add HoH damage once you have enough DP that you've surpassed the action economy limit for FoB. At least, until level 11.
At level 11, you get HoH for free when you use FoB, so you always have at least as many as you can use FoB for. However, since it doesn't interfere with the action economy, you also get it for any remaining rounds, as long as you have the DP (which should always be the case by that point).
Warrior of the Hand
Quivering Palm: This does a large quantity of damage, but takes your full action to activate, so you don't do other damage on that turn. The number of times this is used depends on how much DP is leftover after using FoB. By default, this will be 2 uses per short rest at levels 17+, though it's possible to increase it with some adjustments.
The handaxe build (in red) pulls an early lead because of Vex. I got rid of the dual-wielding dagger because it doesn't contribute much damage, and eats the Vex boost which is better spent on a full unarmed strike. The modeling of Vex will be slightly less accurate for the monk, as it was designed for the rogue and fighter classes, which only maybe have one offhand attack, rather than potentially two. It should still be a reasonable approximation, though.
Warrior of the Elements
Environmental Burst (level 6) is not included, since it's an AOE effect that takes the place of normal attacks. Since AOE damage is impractical to model, I've left it out.
Empowered Strikes (level 17) is a bit like Hand of Harm, in that it's an extra damage die on top of normal attacks. It doesn't have any DP requirement, so it's always used as long as you hit at least once that turn.
Destructive Stride (level 17) is another AOE-like effect which I'm not sure how I'd model.
Both AOE effects likely boost the Warrior of the Elements' general damage potential vs what's shown in the graph.
Vs Barbarian
Here's a fresh comparison with the Wild Heart barbarian.
The monk comes a lot closer to the barbarian at level 17+ with the extra features added in. Overall, it's not as bad as the earlier estimation.
However the flatness of its damage is still evident, though now it's more clearly levels 8 through 16. Only the Warrior of Mercy gets a feature to boost damage at level 11, and the monk's martial arts die also increases from 1d8 to 1d10 at level 11. All the other features monk gets during those levels relate to mobility and defense. (NB: Xanathar's and Tasha's subclasses differ on this, having more 'active' features at level 11.)
Those are certainly useful and thematic, but having such a long stretch, from late 2nd tier all the way to the end of 3rd tier, without any significant increase in effectiveness in a fight, while everyone else is still improving, is likely a significant component about the monk feeling "weak".
The one major factor in the monk's toolkit is mobility, both in the base class, and in most of the subclasses. It's clearly built so that its increased mobility compensates for its lack of direct power. The question is, how do you leverage that in a game that is quite often frustratingly limited in how you can use movement in a fight? Plus having features that often cut your damage in half (use your bonus action) to use them (often for increased mobility).
Anyway, I don't have any answers. This is just an examination of where things stand.
