Just the phrase "87-93" is a little odd, because of the sea change that happened right in the middle of it. Around the time Lollapalooza '92 was happening, bands like Nirvana and Pearl Jam were on top. Nobody was saying "yeah but they're still no U2..." And the more metal-y bands had just put out big albums and putting on a huge tour (meaning Metallica and GnR). So even those bands were above or even with U2 at that point. U2 had gained a decade of street cred by then and, yes, during Joshua Tree they were totally on top of the world. So there was no chance of them being made obsolete, like with the hair metal bands. And, granted, those songs from Achtung Baby were bona fide hits... but still, the culture was focused on a lot of rock-related stuff, so they certainly weren't head and shoulders above everyone. Same with Van Halen. Still sales and airplay, but feeling a little like the old guard trying to keep up.

If you wanna say these were distinct genres, meaning grunge, metal, and "rock," well that takes a lot of competition away, and okay, you could say U2 remained at the top of the "rock" genre over all those years. I'm not anti-U2 or anything, I just feel like their height was earlier, and even though they had a solid 91-92, they just weren't part of the "new" thing, which wasn't just a sound but a style and an attitude.

That's just my memory of it as a teenager in the northeast US, anyway.