This is pedantic, but I need to point out that when Brubaker worked for Marvel it wasn't bought by Disney yet.
In the case of Brubaker, he was working on a title (Captain America) and reviving a title (Bucky Barnes) that was generally speaking not in the top tier of the Marvel line, nor was Bucky a character that was iconic. Let's put it this way, Bucky being killed off (which was done in a quick flashback) didn't provoke a reactiion the way for instance Jason Todd's death in the '80s was a big deal or Superman's death in the '90s was a big deal. Well before he worked at Marvel, Brubaker made a name for himself at DC and in independent comics so he was a known name at the time and not his first big gig.
Let's put it this way, suppose me, my friends or my kid (i am not old enough to be a Dad in any case) is an active freelance writer of fiction,
-- I'd push them to get himself an agent and a lawyer, and also tell'em to make a go in screenwriting or legitimate publishing.
-- If Disney comes and offers a substantial amount for a work-for-hire deal and they are working on a TaleSpin TV show revolving on Kit i.e. a TV-only character and then through my actuaintance becomes a big breakout and crossover star, then I would ask them to summon the lawyers and get a bigger deal.
After all that's what happened with Don Rosa. Don Rosa is an artist-writer who writes the best Uncle Scrooge and Donald Duck stories after Carl Barks. He is work-for-hire and studiously works on pre-existing characters, avoiding creating anyone new when possible. His comics are popular, they sell well, a graphic novel even wins major awards. And Disney start promoting his run using his name without his permission and give him no additional money or health benefits. Meanwhile his run is harvested by Disney for the upcoming Duck Tales 2017 show.
https://career-end.donrosa.de/
Don Rosa as he points out knew the score, new the deal, and he still feels betrayed and humiliated for his lifetime of passion.