the growl can also be in the amp, depends on how you drive them, plus some amps, specifically Gallien Krueger, are well known for their growl.
Tube amps are still alive and well in bass-land, but as others have pointed out, they're big and heavy esp compared to tubed guitar amps because you need more power for bass. And that means more tubes and bigger power and output transformers.
I see more than a fair amount of people out there gigging the big SVTs, Mesa 400s, Traynors, and the rest. There is a certain something about them that works for a lot of people.
I've gigged both for about 40 years and I largely rely on SS amps because that's what works for me most of the time.
I still, however, use a blackface Showman through a modded 2-15 Showman cab to get
that sound when required. You can get almost there w/the hybrids, but IMHO and IME, you need both the preamp and amp sections in glass to get the whole enchilada. If you have the appetite for enchilada, that is