When it comes down to animation, even though the movies and anime have "separate" teams, it is undeniable that the movies poach all the top talents.
There is no "poaching" to be had here.
Animation, and subsequently, anime in general, is a field primarily filled with freelancers. Even people from overseas can get hired. It's usually never really an issue of having the "right" people for the job unless new hires are working on the seasons, and even then, it's not like "new hires" are suddenly inept at doing animation. There are LOTS of skilled animators.
Chances are, you probably can't even single-handedly recite all of the notable animators that worked on this anime BY NAME, outside of Nakamura. There's no way of telling just how many employees work double time between the movies and the seasonal anime outside of reading the credits (and really, who has time to be doing any of that?)
If the seasonal director for the first 3 seasons' departure from the anime did affect Bones, I suspect that it was more or less unnoticeable, and had no play in season 5's "drop" in quality.
Overall, I would argue that the "skill" of the animators has little to do with how well something is animated and more to do with time constraints and budgets. There have been a lot of scenes and shots resurfacing on the internet of scrapped season 5 animation. They're all spectacularly animated, it's just that for unknown reasons, they weren't put into the anime. I theorize this is solely because Bones was under heavy time constraints. Either that, or I guess censorship.
Let us also dispel the idea that for whatever reason or purpose, the movies suddenly detracted from the animation in the anime.
This is illogical and blatantly fallacious, because if we're going by how well something is animated, and judging an entire season of production based SOLELY on that, then it would be more logical to give a complete overview of the material that we're reviewing.
Not a few scenes, that for the most part, only make up a minute or two of run time when grouped.
No, you review ALL of the material.
And what does the average of all the material show us consistently? Good animation.
It is very telling that I've yet to see anyone, outside, or inside of the fandom, really do any of that, outside of rag on how Bones ****** up a minute's worth of animation.
All of the anime seasons, yes, even season 5, are consistent with their animation. Whenever you hear some dumbass on Twitter complain about MHA's animation in season 5, they almost always leave out the first half of the season, because everyone understands on a subconscious and fundamental level that the animation was so good during that part of the season, that it is impossible to slander it.
Anybody who says that it wasn't good is either lying to themselves or just genuinely too ignorant to give it credit. I know it because I was around to see it from my very eyes.
The first ten episodes of that season had people salivating and foaming at the mouths because of how absurdly good the animation was, even for scenes that had little importance or relevance to the story. You could argue that the beginning of the season, in terms of how well-animated it was, tops every other season to come before it, except maybe the seasons 1 through 2.
I'll be
very pleased to provide examples of what I'm saying here if need be.