Is your feature request related to a problem? Please describe.
The mob spawning system is designed for a singleplayer. With a global mob cap and around 10 players the mobs will be spread out to everyone. This will cause the global mob cap to be filled up quickly while the individual players get very few monsters/animals. If you are the only person online mob spawning will be normal just like in vanilla singleplayer. Animal spawning is also affected by this problem. Most animals encountered on servers are ones from newly generated chunks. Once you clear an area of animals very few will spawn.
Describe the solution you'd like
An option that will use an individual mob cap for the chunks loaded by each player. This way mob spawning will be very similar vanilla singleplayer while multiple players are online.
This would be really good, on our server as well it's always hard to get mobs to spawn when there is a fair amount of people on.
I have been working on this, just a plugin for now.
https://www.spigotmc.org/resources/distributedmobspawns.67599/
I still need suggestions on how to handle chunk generated animals. It doesn't perform (in terms of speed) as well as I hoped it would. Working on fixing these issues and eventually creating a Paper patch to do it efficiently.
Most helpful comment
This would be really good, on our server as well it's always hard to get mobs to spawn when there is a fair amount of people on.