Speed command if it was buffed anymore it would be pretty overpowered. It used to be higher but you would see players run across the map in seconds.
Dead Thread
I agree with Zack
It's for personal skills to see if you can reach a certain level.
It's as if I got my teacher to help me with my GSCEs that wouldn't happen.
It doesn't seem action will be taken
Next time don't add players to your plot
Use the command /plotme deny (playername) if someone is annoying you
Try to get a screenshot or a video of them griefing since you state you saw them