Oh wow, this makes so much more sense now!
I was super confused how kbin seemed soooo much more efficient than lemmy, because kbin.social seemed to handle ~120k users similarly how lemmy.ml handled ~35k.
At the same time I knew the server config of lemmy.world, EPYC Rome 32 cores 128GB ram, which was completely fine at ~16k users.
Now I learned that lemmy.ml (35k users) only just moved to a baremetal server, and it's not a huge one at that, it helps paint the picture: 6 cores 32gb ram
Now that it seems like kbin.social is not at 125k users, but at 25k, this makes much more sense, even though I don't know the server config of kbin.social
Well, I'm just forgetful.
kbin is (probably) running on a CCX41 or CCX42 by Hetzner, judging by a fairly recent ernest comment, so if i understand this right, it's 8 cores with hyperthreading and 64gb of ram