I'll explain why

Well I feel like the collector would be a bit more difficult but I get your point

Yeah, although he is the final boss doesn't mean he should be the most challenging

3: The collector... although the final boss in the main story... shouldn't be as challenging as let's say Beldum or Shadow Wymar, the Collector will probably be able to be reasoned with mid fight too.

2: It's beldum, Beldum is a sadistic god who will want to kill everything and anything in It's path. It can't be reasoned with.

1: Shadow Wymar, Shadow Wymar is your shadow and the secret final boss, he is only unlocked after doing every side quest and besting every boss (including secret bosses). He will basically act like Inner agent 3 but ramped up to dark souls level difficulty

Oh NAWW windcar is forced to reconcile in a battle with a personification of her actions

i feel like the collector would be an easier boss because his bossfight would mostly be cutscenes

Oh yeah G-Man is nowhere near on that list