You are partially right and partially wrong in my personal point of view.
WRONG - It is up to the coach criteria on how to use their players, people can only assume without been certainly informed on how things are being cooked inside the kitchen. I can't blame or judge on any coaches' desitions. I think LAFC is the club doing things better than the rest. Nobody can judge the overall development just for one oversee.
RIGHT - MLS academies have the marketing power to scout the best players around, that is inevitable, no other club can compete with that. It is just a subconscious society reaction. Society tent to believe that MLS does better things and of course, it is very attractive to wear MLS jerseys. MLS Coaches developing... idk. some do, some don't. from a coach POV, it is relatively easy to set back and be one more fan or spectator of his own team. having a very talented roster make sometimes or a lot of times lazy coaches. I don't want to finger point anyone, that is not my responsibility. results are visible out there.
My concept of good development is when you see teams starting weak, midseason ok and end of the season strong, or strong from start to finish (as LAFC last season) That will tell the training, the coaching the chemistry, the structure, etc.. improving to the level desired. Unfortunately, after every season, the hunting starts again and the knowledge earned start to have deviated.
My thumbs up for Pateadores, Strikers, Surf, LAUFA, FCGS, Arsenal, TFA. They might not be the best, but you can see they repetitively progress every season.
Again, this is just my most neutral POV. you might have a different one that I will always respect.