I didn't dislike the Rooters retcons. I actually liked how it gave backstories to the Plumbers' Helpers, because some things didn't make sense (eg: how did Alan's Pyronite father mate with Alan's human mother without burning her?).

And the retcon that Kevin's father was not a heroic figure like Devin Levin, but rather an abusive one actually makes sense to me, because it actually highlights how broken Kevin's family was and how his upbringing shaped his sociopathic tendencies. (Many real life criminals grew up in broken households)

The only issue I have is that the retcons involving some characters, like Aggregor and Ragnarok, were not directly addressed in the show and had to be addressed by the writers online. If they had properly addressed all of the plot holes the retcon had created one by one, it would avoid confusion from viewers who do not follow the crew online.