"how involved, cooperative, and enthusiastic Marvel were for UMvC3"

I don't know, man. I remember watching clips of "Making of" videos of MvC3, and Capcom did say Marvel was a bitch to work with even back then, though obviously not to the degree of how it is today.

One thing in particular that really stood out for me was the design of Dr. Strange. That alone Capcom had to re-submit revisions for like 20 million times going back and forth with Marvel because they were so picky/changed their mind last second every time.

Also Marvel basically gave Capcom 0 freedom when it came to which characters are making the cut into the game (MvC3). Most of Marvel cast were picked in order to make people more comfortable/aware with those characters to promote MCU. (this was back when the MCU plan just started rolling out) I remember all my friends going "Rocket Raccoon? Who?" at the time, but now everyone and their mother know about Rocket Raccoon.