the worst you could accuse Kurzgesagt is that they have sloppy research on sponsored Videos

Oh boy. If you think that's the worst thing you can accuse Kurzgesagt of you must have entirely missed the whole Coffee Break drama, where not only did Kurzgesagt reveal himself to be a complete dishonest arsehole in his private commications with Coffee Break, he also stood by while a whole heap of his fellow large creators sicced their audiences on a small-time creator who was putting out really interesting stuff.

Plus, unrelated to all of that, his former business partners at Standard/Nebula do not have positive things to say about how he completed himself there. Supposedly he and CGP Grey saw Standard as a way for those of them who got in early to essentially leech off of the newer creators as Standard expanded, and when the other creators wanted to keep expanding it in a way that way mutually beneficial to all, those two creators tried to shut down the whole thing. It only survived because the others agreed to buy them out.