We have a few Survival Realms on Realms plus, and the public Realm has cheats enabled to allow the Mixer mixplay stuff to work. The world is set to make people members when joining, and they are by default placed into survival with no rights to use commands/cheats.
However someone joined recently, and initially asked if cheats were enabled. While showing them around the realm we were at Y=3, and they started breaking bedrock using a diamond pickaxe in 1 hit. Using /kill playername killed them since they were in survival.
This sounds similar to