Jim Shooter was editor in chief at Marvel from Jan 1978 till he was fired in Feb 1987. Byrne definitely was a company man as you accurately describe in his 1975-1985 Marvel years, and probably would have been forever in other circumstances. In particular I recall an editorial Byrne wrote in FANTASTIC FOUR CHRONICLES (from Fantaco in 1982) where Byrne was very happy at Marvel, and said he felt like Marvel (or any comics publisher) was entitled to a larger share of the profits, because Marvel takes on the greater risk of publishing a title, and if it sells or doesn't sell, he as a writer/artist gets paid regardless, and if it doesn't sell the publisher takes a loss.

The problem began in that, while he loved being at Marvel, Byrne wanted to do a Superman run, while maintaining a friendly relationship with Marvel during his absence. Even after announcing he was leaving to do Superman, Byrne planned to draw FF through issue 300 regardless, and gave very far ahead notice, to leave amiably and presumably return to Marvel after. But then his editor at Marvel kept making nit-picky revisions to harass him, which had never been requested before, so Byrne saw what was happening, took the hint and abruptly quit, with issue 292 or 293.
And Byrne also abruptly stopped his writer-artist runs on INCREDIBLE HULK, and on the "Last Galactus story" in EPIC ILLUSTRATED 26-31 or so.

A similar jerking around happened with the George Perez-illustrated JLA/AVENGERS planned crossover special, that was delayed and delayed, and finally scrapped in 1983-1984, that Dick Giordano wrote about with anger in his monthly DC editorial, in 2 parts over 2 months, concluding with "apparently someone or several somebodies at Marvel don't want the project to be published."

So yeah, there was definitely some bad blood between Byrne and Shooter, and it followed a pattern. And I guess when Byrne was frustrated with DC over his Superman work, and Shooter was no longer editor in chief at Marvel, Byrne was willing to come back to Marvel under new management. And incredibly, took over Shooter's personal signature book STAR BRAND, and injected some brutal metaphoric stuff to Shooter's downfall within the story.