Especially when doing my doom/shoegaze/doomgaze stuff, amps are essential. Even half stacks in small venues, which for ALL us players AND fans, are still actually essential to the experience. It's not just about tonal qualities and volume, it's about how much it disperses throughout the space. I was even running a Thunderverb 200 with volume at 2 o'clock and it sounded glorious-not just to me on stage, but audience and sound engineer all had HIGH compliments for the sound. So yeah, it may be genre specific, but at at least if you're dooming, you better come correct, and that means big f'in amps. Granted, fly rigs are necessary, even for doom bands-saw a fabulous Chilean doom band here in Seattle called Quatrro (IIII). Naturally they went with ampless fly rigs, and yeah they killed it. Great set, tone was there, but it was a bit of an uncanny valley. Sound with far less physical presence and dispersion. It was weird.
I'll also add that when I was gigging in a classic soul band for weddings and whatnot, I went both with amps and ampless at various times (I was also tastefully using a Fender Princeton, as that's clearly not the gig for big f'in amps, or I was using the UAD Dream '65 straight to board). I could get that UAD set up to sound pretty great, our drummer/band leader was psyched at first because he liked the super clean stage for the sake of showmanship, and he had his own mix into his in ears he could control himself. But after a while, even he was like, "I want you to bring an amp again." So yeah, there are times when the ampless/fly rig route is the way and it can certainly work, but, unless your sound is only capable of being produced through a PA setup, amps are rule.