Hi there. The End is currently in a grey area in terms of rules.
The End is unprotected and has PVP-ON, and I have always refused to protect anything in The End.
This means that The End has always been like a permanent Outlands. That means no griefing in-use structures, but PVP is on.
The rules of The End are changing VERY SOON, however, with more info on that to be posted today.
Regardless, in terms of this conflict: unless CJ broke blocks, I'd say he didn't grief. Furthermore, CJ isn't preventing you from "using The End", he is just PVPing you. You have the option to fight or flee. He is not punishing you. He is just fighting you (in survival mode like everyone else), regardless of his status as Staff or not.