But you can already see the hurdles of large instance like lemmy.world.
The costs are so immense (probably because of some unoptimized code), the software isnt “ripe” enough that it can be left alone for few months and have it run smoothly. It needs permanent monitoring and maintenance. And that doesnt even go into the moderation issues.
TF2? Tbh thats not a bad thing, as how unoptimized TF2 is. At least if you did this on a public server and not just a singleplayer game.