https://github.com/OneLemonyBoi/MiniUtilities/blob/main/src/main/java/onelemonyboi/miniutilities/blocks/earth/BlessedEarthBlock.java#L77
This line checks for the amount of IMob ( hostile mobs ) and therefore passive mobs will never stop spawning.
Also for each player on a server the mob cap goes up by I think its 70 (for hostile mobs), so we enough people on the server your earth will just stop working

https://minecraft.fandom.com/wiki/Spawn#Java_Edition_mob_cap

Yes so hostile is 70 and passive is 10.
So maybe not check the servers cap but the area around or something? if that isn't to much of a performance cost