Where the actual fuck did you pull this bullshit from?
"Ozmanthus wouldn't learn from the fuckups of other people and would just do it again, despite experiencing the failure from the other side. And then have to kill people he was personally attached to."
If he did get clearance he probably would have gone for a larger group so people could take a break. When I was reading...Reaper? I don't remember. I was struck by the fact that Ozriel couldn't retire.
There was no one else who could do his job. No one to take the burden. So when an iteration failed he had to kill, and kill, and kill. To the point where even he got sick of it.
Makriel wants to turn him into a slave. That's what the executioners were treated like before. Hell. Something like that happens in Threshold. Guess what happened? The bound person had the emotional reaction of wanting to murder the Abidan.
Predictable reaction.
That Ozmanthus totally wouldn't predict
An important distinction to make is that Ozriel is not actually asking for his own division of helpers who help him reap worlds. Makiel would probably approve that, because Makiel likes the idea of a reaper but hates Eithan specifically. A division of helpers for Eithan gives him the chance to set up a new Reaper who is less of a renegade. But if Eithan actually wanted to retire, he could! The important thing isn't that he specifically has to be the reaper, the important thing is that there must always be a reaper. So long as he set up a suitable successor, he could absolutely hang up his mantle and quit. Eithan was a one in quadrillions talent to find his own method of wielding the Way in the mold of the original court of seven, but taking up an existing mantle, while still an enormous achievement, is probably significantly easier and thus could be accomplished by anyone dedicated enough with the right training. We know this is possible, because without even soliciting Eithan's help Makiel got pretty far making substitute scythes on his own, presumably with the intention of getting his own Reaper of Worlds who would be loyal to his agenda. All of this to say: It isn't that Eithan can't retire, it's just that he has to give a suitable notice first and leave behind a successor.
The thing is, for all that Eithan has many issues being the reaper, and many more issues with his coworkers, he doesn't actually want to quit. He just wants to stop having to reap worlds he feels could have been saved earlier, hence his initiative to restart the Executors under his leadership. My assertion is that this would have crashed and burned if it was approved. I don't think it's controversial to say that Ozmanthus, for all of his skill, was not really a people person. I think the specific instance where he begins to learn to be better in Canon is during the Uncrowned King tournament, where he truly chooses to confide in Lindon and Yerin and then asks, without scruples or deeper schemes, for their help. (This was where he wasn't sure whether to really try to win against Miara or to throw the match.) It wouldn't shock me if this was the first time in his eons long existence where he actually confided his worries and asked for help, and it's a remarkable step for him. Yerin even explicitly tells him here - for all of how she's been through several books worth of shenanigans and adventures with Eithan, she doesn't even slightly trust him, because his goals are too mysterious and he never confides anything of his thoughts to make himself known to her and Lindon at all.
My point is that this step forward is something he only learns to do as Eithan, having gone through several years of character development, both on and offscreen. He has to suffer the terrible defeat of losing his family and Monarch to be humbled and even start to try and loosen up. I don't think he would ever make himself vulnerable in that way to his subordinates were his request for a team of Executors to be granted. Instead, I think he'd puppet them around, making games out of their training but never gaining their trust, in the same way Yerin never trusted Eithan until he opened up. Inevitably, any team that does not trust its leader will become dysfunctional, especially one with such weighty responsibilities and such a lacking support group, since the rest of the Abidan will be actively suspicious of them.