You're making those mechanics sound WAY harder than they were. Also raid addons were around in Vanilla. People just had less experience with the game so fights felt much harder. Considering you can do Mythic bosses at the moment with absolutely no addons doing Vanilla bosses with no addons was extremely easy. It's literally down to the fact the game wasn't over a decade old and the general playerbase was absolutely clueless.
Tbh it sounds like you're the one who didn't play much Vanilla WoW.