So, I decided to take a look at the game's damage average since the numbers already posted seemed a bit off. Talked to Tal about it, and after some toying around with spreadsheets we both figured out how to actually properly factor in self-damaging moves. Basically, self-damage moves can be reflected well by subtracting
(Kill point) * (% MHP self-damage)
off of each character's damage. This is non-trivial to calculate because knowledge of the kill point is needed to calculate what said kill point is, but repeated estimates will converge to the correct average. Tal came up with a formula that you could take the limit at infinity and get the average directly, but simple brute force suffices for the precision the DL needs (i.e., to the nearest point of damage), so that's what I used. Anyway, math details aside, here's how P4's looks:
Auto-Taru, Souji included
Souji 1400 - 1018*0.125 = 1273
Teddie: 361
Yosuke: 329
Kanji: 518 - 1018*0.2 = 314
Yukiko: 281
Naoto: 148
Chie: 143
Average: 407
Kill point: 1018
Yeah, this is higher than the previously listed average. Note that, if anything, this average might be an underestimate — a 3-turn average would make use of Power Charge and Mind Charge (Chie's damage skyrockets in particular) and thus be higher, or you could also argue that since Souji has two full HP bars that his % self-damage should be halved. But anyway.
Other averages
Non-Souji averages are listed for those who feel Souji is too much of an outlier when considering the damage of non-Souji PCs (I'd have to play the game to decide how I feel, there, but based on hype for Chie OHKOing, this is probably a common enough interp). Non-Auto-Taru averages are listed if the boys want to set up for defence and/or if at some point in the future P4 defence is actually determined to be effective enough for this to be a default. For space reasons I won't list out the calculations like I did for the first.
Auto-Taru, no Souji: 274 (685 kill point)
No Auto-Taru, Souji included: 312 (779 kill point)
No Auto-Taru, no Souji: 221 (552 kill point)