Not really now that they've coordinated their servers and playtimes, also the mass server merge helped. I mean people think in order to be alive it needs to have millions of players which is just not true. A successful MMO before WoW's time didn't even have a million players. I think EQ hit 500k in it's peak. People act like Classic Era might as well be dead and I couldn't disagree more. We always knew it was going to be a niche community left over. The whole point was to undo the mistake of not just having a Legacy character option to begin with in 2007 and ever expansion thereafter. Kind of odd that you could make a pre-expansion character in Diablo 2 in 2001 but not with WoW in 2007.
Now the boneheads at Blizzard are making the same mistake again with BC. Granted SoM does kind of split the community further, but if they did SoM correctly (no transfers from Phase 6 servers to screw it up and way more than 40% experience which they did increase to 100%) then it would have been fine. But again, we always knew these would be smaller niche communities, the people who missed out, or got sick or didn't have time for Classic in 2019/2020 and really wanted to play, the speed running community which is actually larger than most speed running communities. 5-10k is fine for a niche community. And Blizzard should be smart enough to leave every version of Classic up, eventually they'd be farming about a million players, assuming the Classic experiment went all through the expansions. The entire thing should have been built into Retail anyways, just go through a time portal and boom you're in Classic mode with all gold/inventory separate, all completion data and stats/skills/talents the way they were then.