Why have we assumed that undertale has the same idea of the player being the soul

That has never been even implied I feel like it's just frisk gets the nice or evil from you once you beat the game

chara and flowey talk to the player directly after finishing a route

wait, misread

I don’t think I understand what’s being said here. Are you saying Frisk is separate from the player like Kris is?

Yes, because Flowey directly says "let Frisk live their life."

implied, perhaps.
but I think it's easier to assume.

This is more for theorys because I don't like a theory that has to use another theory that isn't confirmed as evidence

ok