This whole notion that raiding is what the entire game is about and that the "real game" doesn't start until endgame didn't really solidify until some time after WoW was released. This peaked around the WotLK/Cataclysm era when Blizzard started making design decisions around "herding" the playerbase towards the latest raid content. The early era of WoW was still somewhat more leaning towards the classic MMORPG mindset of just having this large virtual world. This mindset started to come back for Blizzard with MoP when they realised that perhaps not everyone was that interested in raiding.
I started playing in 2005 but never really got my feet wet with raiding until the expansion. I spent a lot of time during vanilla just leveling different classes and it took me almost a year to get my first dedicated level 60 I could stick with. I imagine a lot of players had a similar experience. Leveling was a much more drawn out process back then since it wasn't just considered inconsequential padding before the "real" game start. You were out in the world and met plenty of other people doing so, and I imagine this is where many got their favorite vanilla memories from. I know I did.
Ah, I think that's a difference in play style, then; as someone who steadfastly stuck to
one character (and indeed, still do, convenience alts aside - my attitude is that I'll level a serious alt once I feel like I'm sufficiently good with my main), it felt like when I hit the cap the only real option to continue PvE progression was to do dungeons leading into raiding leading into more raiding. Unlike nowadays it did feel rather like raiding was the only real long-term option for endgame for PvEers, but you'd absolutely get a different experience if you preferred to play in a way that didn't
get to endgame.
I did feel that I had more options
at endgame to entertain myself outside raiding in Wrath than I did in Vanilla.
I'm not one for "The real game doesn't start 'til endgame" - I *love* the levelling process - but it's more that, in Vanilla, 'When you *get* to endgame, your options are limited'.