I wonder how Planetside 2 does it, considering they have quite big battles at times.
As for if it is possible, absolutely. Erigato has made some like knuckol.club but afaik he didn´t use constructs multiplayer plugin.
This might also be interesting, I´ve stumbled on it a while back and now dug it up again, the dev talks a little about diep.io and agar.io But it´s also from 2016 so take it with a grain of salt.
https://news.ycombinator.com/item?id=13266692
But he hints at github.com/uNetworking/uWebSockets
Thx for mentioning my little game,You are correct i would never use the official multiplayer plugin for things outside of a local co-op game,The official multiplayer plugin is indeed good for somethings but lacking basic things like interest management that can easily be created if you follow along a basic guide like dynetisgames.com/2017/04/05/interest-management-mog really gives it a 1 star out of 5 for me.Using the websockets plugin is more than enough to create a smooth multiplayer experience but it's far from beginners friendly since it will require you to know javascript and have looked into multiplayer architects