To properly stresstest a site you'd need a MUCH larger control panel server or you risk affecting people using the control panel and test accuracy. Even if a new role was added so you could have a dedicated stress test node, proper stress testing usually requires several servers hitting the target at the same time.
Cyberpanel isn't a good standard as they are a garbage panel. Its probably very halfassed as most of their features are. A good example just from their screenshot is that they didn't even bother to add commas to any of the numbers or convert 20,000MB to 20GB...
There are a lot of open source options and some have web UI's that you could use though. Many use AWS or another cloud's API to spin up a bunch of test servers, sycronize them, run test and then spin down all the servers.
