In 9.5.9 release note it was declared that a relay can host 5000 clients but it has again come down to 1000 clients, it is not officially declared in written but have heard. If you are not having any performance issue then it is ok but for the best practice i would suggest you to keep 1000 endpoints reporting to one relay for better performance.
Totally agreed with @FatScottishGuy if you want to increase the scaling you need to increase the hardware specs of the Relay server to avoid performance issue.
Whether the relay hardwaremustbe improved really all depends on what the hardware is now…thr Capacity and Performance guide already referenced should help.
The most important parts of relay scalability mode are actually in the OS and Relay settings.