the battle royalification of games is annoying for sure, but saying it started with fortnite is giving epic games wayyyy too much credit.
fortnite just ripped the entirety of PUBG but with cartoon graphics and worse shooting mechanics. and even PUBG was just taking the lead of minecraft hunger games which was popular YEARS before either PUBG or fortnite were around
except minecraft hunger games was good actually. it was fun and it was just a single game mode that some minecraft servers implemented, not the whole game. there are a ton of server minigames that creative minecraft community members come up with, hunger games just happened to capture everyone's attention the most, and then devs noticed and decided to capitalize with stuff like PUBG
Modding was still allowed back then so yes, if you wanted
i don't remember quake having robust enough netcode for that.
I think UT2K4 could handle 32 people? Yeah the scale wasn't quite what it is these days