This hasn't been my experience at all. I'm curious where you are seeing that, because in other conversations on TB, the cesspool that is facebook, and IME i see the exact opposite - in fact, I'm all Class D right now and couldn't be happier with my tone - and I have been through A LOT of amps and preamps. The portability is a plus, but I wouldn't use something that I wasn't happy with tone-wise. I suspect most other bassists are the same.
Also, for the past (at least) 3-4 decades, arensa, stadiums, large venues - all class D. I would think that if class D amps inherently had poopy tone that they wouldn't be used for these places.
Class D amps aren't missing tone, that's a fallacy, and again, I've never seen a discussion missing tone. Maybe we run in different circles ...