Point 2 is the exact contrary of the truth: a party of six works better in turn-based combat than it does in real-time, especially on any system that requires any degree of participation above “EVERYONE AUTO-ATTACK!” and with an appropriate difficulty threshold.
Don’t even take my word for it:you can go and check Josh Sawyer himself claiming that they lowered the party cap at 5 in POE 2 precisely because some people were having a hard time keeping track of the party and he explicitly stated he wouldn’t have done it if Deadfire was a turn-based game (which hilariously enough it became, at a later date).
Point 1 may have some merit, but if anything it just adds to the pile of arguments about why the UI sucks and should be revamped. It’s not a GOOD argument against the extended party.
Point 3 is whatever. Basically a tautology. “Larian is right to do X because Larian has a history of doing X”.