Chuck Dixon actually talked about Didio on his podcast today pretty openly(since, as he says, he has no bridges left to burn)https://youtu.be/cIo91pKrNJ8?t=1368
basic run downs are, Didio loved to micromanage, liked to take credit for anything that worked well(and was upset if he wasn't involved in a success), and tried to handle every little thing in DC.
Dixon suspects he was fired for working too fast for Didio to catch up and working too far ahead of Didio's planning. Granted it could be unreliable narration, but considering this was before Dixon got as public about his politics and that most editors have nothing but praise for him as a worker, I trust in him. I mean, Larry Hama likes him.