Well...
1) There is much less to talk about Classic than BfA. Classics is something that was already done and is known.
2) There is so many trolls stirring the "let's change this and this" that the forums have had a pretty toxic atmosphere. I guess we'll have to wait for them to get bored and leave, and the many anti-Vanilla posters who aren't exactly trolls but come here to just say how much they hate the game to do the same, before we can have actually interesting discussion.
3) Nobody but delusional idiots ever expected Classic realms to be bigger than current ones. I expect Classic servers to hold between several tens of thousands to a few hundred of thousands people at best. That's still LARGELY enough to pay for their cost, but that's not about outcompeting BfA.
I DO believe that a modern WoW with the original game design philosophy would have been more successful than what current WoW has devolved into, but I certainly don't expect Classic servers to be that.