One of the core things that is documented and public is that "SuperMega" got mistreated and borderline abused when they used to be his editors. Mark even clarified on his regret on Facebook. If you Google it, you'll find dead links affliated with the nonsense via /rantgrumps.
When they bailed to GameGrumps, Mark was pretty much blacklisted by the Grumps and has not been featured by select circles since. In that time-frame, SuperMega was also getting a nice plug by LPin' with OneyPlays. Since than, they've (SuperMega) have gone solo and cut ties with just about everyone mentioned here.
SuperMega got lucky in this instance. They had a creative platform which was growing and place to share these problems openly with assured support. "Johnny Nobody" who edited on the cheap back in 2017? He'd never survive if he went open.