>>18173294And mega tyranitar is a complete upgrade over its normal form too. There is no reason to run regular tyranitar over it unless you want a specific item on their build.
The thing is, it just doesn't do all that much. +100 BST to a pokemon alone doesn't justify spending your mega slot on it. There needs to be something more, or else you would do better with a different mega.
I'm sure some teams will run it, just like some teams run mega tyranitar, but they're going to be in the minority and other megas will continue to be preeminent over them.