Based on what research is that universally true? (Other than base physics like statistical mechanics.)

Base physics is all we need to know it is true. Souls are unphysical and we've had reason to be pretty confident about that for at least a century.

Yes, physics determins how phenomena work and aggregate but that doesn't necessarily support the specific claim (and we also don't know "all of physics").

Doesn't support the specific claim that souls don't exist? We know how atoms/waves interact. We have literally no reason to think there is some other soul-based mechanism.

Of course, maybe induction is false and gravity will reverse in the next 3 seconds after writing this comment and God will reveal themself to us. We have no justified reason to think otherwise other than the general principle that things behave the way we observe them to and will continue to do so.

I see no need for a soul - you brought it up, not me.

What would it mean that you are 'what you're doing' is not statistical/arising from base interactions - if not that there is some non-physical entity resembling a soul? You're suggesting some sort of non-material component of humanity, yes?

If not then I'm not even sure what the disagreement is.

Base interactions need not strictly create statistical results in the end.