Scott Mosier was essential to Kevin Smith's career
Tusk, Red State and now Yoga Hosers all had good concepts to work from but all three suffer from awful pacing and just stupid decision making all around. Kevin himself admits that he listened to notes and suggestions made by studios in his early years (think the original Clerks ending, the ridiculously boring alternate intro to Mallrats etc.) because they were usually right and because, self-admittedly, Kevin isn't that great at making movies. So while he has a penchant for characters, dialogue and decent plotlines, I think it's safe to say that he overlooks potential blunders quite often and it's good that someone else on the same level or higher than him would step in and let him know and that he would listen.
The last three movies prove that he NEEDS someone to step in and say "Hey, this scene goes on way too long" or "I think Johnny Depp needs to clean up his speech". I know Scott didn't have very much creative input in the earlier films, but he was heavily involved in the editing process (and also came up with the funniest line in Zack and Miri "Can't you see we talkin', White?") It really feels like him not being around has severely impacted Smith's work. Smith's last good movie was Zack and Miri which is also the last movie Scott worked with him on. Not to mention he basically helped come up with the story for Tusk and the title for Yoga Hosers (the podcasts behind both are actually way funnier than the movies).
I'm glad Mosier is doing his own thing because he's an awesome dude and it's cool that he's worked on stuff for Disney as well as really good documentaries that earned Oscar nods. I can understand why he wouldn't want to keep making someone else's movies, but I do believe his absence is a big part of why the last three Kevin Smith films have been so awful. I think Smith's new crew are just a bunch of Yes-Men who wouldn't dare question anything Kevin says, he really needs someone like Scott in the editing room again.
I do see that Scott is producing Helena Handbag if IMDb credits are correct and if that movie is even still being made. That was one of the funniest podcast episodes and it could be a hilariously awesome movie if done right and Scott came up with some really funny stuff. As for Clerks III, it honestly wouldn't feel right if Scott wasn't involved but I'm sure he'll at least reprise some of his old roles.