A buddy of mine that I've been in bands with off and on since I was a teen is a freak when it comes to live sound. When I first met him, he had this cheap, POS drum set tuned so good, by putting bed sheets between the shells and the heads.
45 years later, he knows live sound. I used to be in his current band (80's covers), but since the time I left, he's gotten a killer PA (he actually headlines outdoor gigs in the summer, and runs the sound for the other bands), and his band sounds the best of any local bands around. From the opening notes, they sound fantastic! I mean, clear, tight, punchy, all the adjectives..., of course, amazing drum kit tones, with everything dialed in, mix-wise. He's gotten to that point where he's doing really well, playing the top places in Ocean City, MD in the summer.
I generally don't like to be the guy who goes, "Well I talked to this guy, and he says...", but in this case, I really trust his judgement.
I reached out to him about this shunning of stereo for live sound, and he told me, not only does he use it, I'm the one who sold him on the idea, because of how great my guitar rig sounded when I played with him. He gets to hear a lot of bands, and doesn't play on every song in his own band, so he can go out front and really hear how things sound. By way of comparison, he told me the bands that play mono sound flat and terrible. The best bands aren't the ones with the stellar musicians, but the ones who have the best sound. His words.
It's a fullness-type of thing. And I'm of course not saying to pan the guitar dry signal left, and the delays right. For sure, you wouldn't do that live. But as I said, I've used it live, with great results. If done properly, it's not like people in certain places in the audience are gonna get a bad listening experience. On the contrary- everything will sound better.
Yeah, it took him years to get it right, but with digital boards now having the ability to save presets, he says it's actually pretty easy to dial things in from room to room, especially in places they've played before.
And yeah, it does add an extra element of things to deal with, that depending on one's own criteria, may not be worth the effort for some. But I can't agree with the blanket sentiment of just dismissing it altogether.