A bit annoying that the backstory is portrayed in such a skewed manner (by the author, in the final place).
If that Sleip (as in Sleipnir, of course) demon general had explained that it all rested on a misunderstanding (the demon magically making the generals unable to move or speak when Gholl was told that no one wanted him to be demon lord, so he just left, and gave his kid brother the throne), then Gholl might well still have decided to decline taking back the throne, but he would at least have had more trust for his former closest people (also supposedly close friends!!!). And MC's rant about how a fresh demon lord could be compared to a baby could have been if not cut, then at least modified - I mean sure, cut new people on the job some slack, but the kid brother demon lord Yuigarde was definitely not even close to be ready for the role, pulled around by the nose byt that demon all the time, and it's not a case of giving him time to learn the ropes.
That said, the demon generals have had quite some time to talk to Gholl about what was going on, and they have done nothing, so by this time they definitely can be seen as either complicit, seriously incompetent, or at least really bad friends.
(Well, it's all down to mangaka-san's writing competence ...)