I don't think Biomutant narrator is that bad. Perhaps Americans find his accent annoying? I can see that happening but it did not annoy me. I feel some people complaining about him are exaggerating a bit but I can see some people honestly turning him off.
The game, by the way, is alright. I won't say it's great or anything but it's ok. Perhaps a bit pricey for it's AA quality but it's hard to judge a game value when stuff like gamepass exists. Personally, I'd buy it on a sale but I am simply not a fan of the genre.
I think some people are trying to pre-hate like there is a cult out there claiming it to be the next best thing since sliced bread but it just happens to be the only big-ish game being released this week. People will always have some good expectations about a game they buy otherwise they won't open their wallets.