It was not always like this. You used to comfortably be able to handle 70+ players in a single server before Paper existed (my memory of this is from before like 2015). You'd need to allocate a lot more memory than normal, like 8 gigs instead of the normal suggestion of 1 or 2, but it could handle it without regular lag.
I forget what heap setting I used, maybe it was 2G, but the old 2010 Mac mini I had as a server would lag if just one player was exploring land quickly (maybe by boat). Was online from 1.5 beta to 1.9 release, no more than 8 players usually.
