The LFG system basically killed most social interaction in WoW.
So if you played for that, you got excluded.
They also sort of killed build diversity, but there was no build diversity in classic either, at least if you wanted to raid.
The grinding... I don't miss it. That could have used toning down.
I started playing Anniversary vanilla one year ago. I played through it all and now I'm playing Anniversary TBC. I visited many dungeons. There's no LFG system, yet I didn't find any social interactions in dungeons. I'm pretty sure the whole social interactions thing is overblown. 99% of dungeons is like leader silently invites you or you write "inv holy pala GS 1400" and he silently invites you. You silently run through dungeons, silently leave. That's about it. There are no interactions. Zero. Some people write "hi" and "ty", some don't bother.
If you know you're not likely to ever meet those people again, you don't bother.
as someone who has played since 2004 with only a handful of month-long breaks, this is simply not true.