Sceptic
As a self-professed outsider, you're missing out a lot of nuances here, like the community aspect, which indeed comes up in every second post - as opposed to mechanics, which are actually not discussed very much at all, or at least in any worthwhile detail.
Yes, WoW's vanilla mode lacked a shitton of stuff that it has now, in terms of encounter design, skills and various submechanics; however, lack of LFG, LFR and various other search tools meant that the players had to interact with each others. You had to get yourself attractive to others in order to come to L60 runs that wouldn't suck massive cock unless you wanted to be that last-moment filler; failing that, you had to actually have friends that'd take you along. Point is, you
do not have this aspect now. It's not an MMO, really. It's a hub for a set of minigames based on the same mechanics without really having the "massive multiplayer" bit. The last time I made random friends with people was basically in WotLK - since then, the only new acquaintances I had came through my raid group.
And yes, the quality of the player base
has plummeted, the only spike is at raid group level. The "casual" level is becoming more and more incompetent. I see this in LFR, and I see this in applications to our raid group. People need to put in less effort into everything. Tell me, is it rose-tinted glasses to compare a completion of an L60 dungeon in ~1h in level-appropriate gear, to a 15-minute romp in similar conditions now, in an all-random group LFG? I really don't think it is. When Pandaria came out, there were like 2-3 challenging moments in the whole "endgame" 5-man dungeons worth mentioning, most of them usually having to do with trash mobs. With all the tools and polish of combat mechanics at this point, this is basically like dropping bombs on an ant hill. Naturally, people get used to that, and when/if they get to Normal raiding, they get hit quite hard with the realization that indeed their massive 40K DPS wasn't all THAT much, after all.
Mechanically, though, it's quite obvious that the game has evolved. It was by no means "broken" though, just more, hm, inconvenient in many ways. Unfortunately, somewhere along the way to "convenient", the game got horribly castrated on the community/non-committed difficulty, though.
Edity-edit: Also, if your friends are in HC raiding guilds, they don't really even have to see any of that deterioration, since HCs get the most skilled players absorbed into them. The only place to see the amazing skillzzzz of the general population are in the LFR, if they still might be doing those for whatever reason.