There's a number of valid arguments for why the plane tracker may not be doxxing, and a couple tenuous, but valid arguments for why to ban the plane tracker account.

But no matter how you slice it, this account (and it's owner's personal account) were targeted purely because they irked Musk, and he has given zero indication that he plans to enforce this rule for basically any other account.

I agree with your assessment.

But Musk owns Twitter and he can pick and choose what accounts he wants to allow.

I guess it is akin to me removing unwanted comments on my blog. His site, his rules, policies and ToS.

He absolutely can but he’s going to get called out as a hypocrite when he acts like one.

I suspect we're quickly approaching the point where impotent cries of hypocrisy will no longer be considered even worth issuing. Maybe we're already there. The charge is inert, it does not sting, it changes no minds, and is slightly entertaining to haters, who chuckle for less than a second, and then get on with their lives.