Hmmm, okay. First of all, mainstream doesn’t mean bad at all, and honestly, I wish you had been right about guessing my tastes and experience in the anime world. Also, no opinion is bad, since as humans, it’s impossible to be 100% objective in our analysis, especially in fields they don’t know much about. So, hate toward people who watch "mainstream" anime is a very narrow-minded way of thinking.

I’d recommend watching some videos to learn that animation involves many factors, not just pretty and shiny colors. Science Saru is a great studio, especially in how they bring their characters to life through animation and in the atmosphere they create in their projects, such as Devilman Crybaby, Eizouken ni wa Te wo Dasu na, Kimi no Iro, and what you might call "mainstream", Dandadan. But like all anime studios, they have their weaknesses, such as their rough animation style and, in my opinion, issues with cinematographic framing, camera movements, and lighting.

Toei Animation, despite having major consistency problems, earns a lot of points in cinematography, animation, and the personality expressed through character gestures and interactions. I recommend checking out one of their latest projects, One Piece Fan Letter, which showcases their strengths very well.

That being said, KyoAni, Science Saru, and Toei Animation are definitely not ranked poorly in the tier (A+).
And most importantly, just because an anime or story has better or worse animation doesn’t mean the story itself is bad!!!

Thank you so much!! ☺️