[Yashatari]

I can think of a couple things for this.
Are you considering food buffs like well fed?
Are you remembering to calculate racials?
Ie how vampire stat boost doesnt apply on the character screen but then applies in a battle depending on your essense counter.
Are you possibly running ghost with the +Stat per 10% hp missing? Are you forgetting about that?
I've seen people hit for 400-600(Crits) and 100-150(Non crit)(Both basic attacks.)
There are some people that only take like 40 damage from a 400+ damage attack.
Are you forgetting about materials that add partial slash/blunt/pierce damage?
Can't think of anything else that might be wrong.