Honestly its unbalanced if you had to limit max zm choices since almost 90% of the map, humans are always going to win due to their double jumps or lowered gravity compared to most zm that isnt sting, another point is :
1.Sting is the only one with maneuverability options who's able to catch up with high ground players
2.If sting is limited, i believe all other zm should receive a buff to its gravity or damage
3.Sting is the only one capable of deleting alot of armor from a high armored player without the use of knife blink trick which not many player knows how to pull off
4.Other zm that is an occasional pick like light zm or Tesla has its own niche that even vips tend to choose sting over them due to not having gravity
5.The only way to make all zm equally balanced is if the server is purely no armor, infect on hit just like cso, but thats not going to happen i believe because of how zp maps are designed to be played
So its a -1 from me