I’m just coming back so trying to understand what all has been done to the game.
The Classic Era servers are from what I understand, fully unlocked/final pre-TBC patch with all content available etc. This is also where level 60 characters were cloned to when the 2019 Classic launch moved on to TBC. Is that not correct?
Really the main things I can think of are missing out on the opening of AQ and the important changes to the game as new content is opened for the patch. If my memory serves correctly, a faithful reproduction of “Vanilla” also means some changes to classes and talents along the way which are non-trivial.
The issue I have with the seasonal servers is that from what I understand everything is sped up so you can do it all in a year. In some respects that’s fine and even attractive if you have time to go ham on Classic.
It’s a simple fact in Classic/Vanilla that gear > skill for the most part in PVP and that many BiS geared players mixing with returning ones is a bit imbalanced. I suppose you could make the case that this is semi-realistic because despite everyone on the forum claiming to have cleared C’thun and Naxx in '06 we know that it was really like 0.5% of players, and they rolled casuals like level 50s in greens lol.
Almost forgot, gold. There is too much gold in the game from what I can tell. Way too much.