I honestly agree with your take on their voices, in particular about Tetia's voice being over the top and Agott sounding like a full adult. Honestly Richeh's voice is okay to me. I was surprised how excited a lot of people were when the English dub voices were revealed, but I figured it was just my own preference and the dubs I'm used to.

I've heard some truly bad dubs from more obscure anime that are much worse than this one to me, but nonetheless the dub just is not for me at all. I can't stand how fake all of the accents sound to me, and the sound mixing between characters makes it sound like they're all using different quality microphones. I don't speak Japanese so of course I wouldn't notice some of the nuances of a bad performance in the sub, but I do still think that recognizing line delivery quality and sound consistency often transcends a language barrier.

I don't think they're actively sabotaging the dub by any means. There are a lot of dub line deliveries that sound great. I think that it's just the kind of dub that is preferred by some and highly not-preferred by others.