Well, tubes never really left the guitar world, as many people,particularly pros, favor the warmth of tube distortion and would seek out and maintain used gear. Tube amps were often ridiculously cheap in the '70's as amp manufacturers focused on more modern transistor-based circuit design. Unfortunately, transistors have a nasty habit of square-wave clipping when they are overdriven, which just sounds ugly. It wasn't really until they began using audio modeling in the late '90's that transistor amps were able produce ear-pleasing distortion curves. That's not to say that all transistor amps are bad, which is certainly not the case. It really depends on the musical application. Transistor amps are actually preferred for applications that require no distortion, like pedal steel guitar or many jazz guitar styles.

As far as recording studio equipment and high-end audio equipment, Yes, tube pre-amps really became a thing with the advent of digital recording in the '90's, as they were/are used to breathe a life back into a "cold, sterile" digital signal.

I have an old 250-watt Kustom tuck & roll bass amp that sounds like thunder. But yeah Kustom did pretty good as far as solid-state amps go. Interestingly, while Fogerty gigged primarily with a Kustom stack, much of his CCR output was recorded using Fender tube amps.

Also, Kustom was re-booted in the early 00's, and began building new-design tube amps in addition to new-design ss amps. As a matter of fact both of my main gigging amps are modern Kustom tube amps.