Tyranitar Bite Fireblast

I'd work on another one. Fire blast seems like his clear worse charge move. Very few attacking a TRex on defense that would take SE from it (maybe a pinsir, with SE and STAB bug or double SE fighting). A lot of options resist it (double fighting Poliwrath tears through TRex at 1/2 the CP).

On offense, you are basically just using him as a bulk attack. Few times fire is good on offense. Even when it is, flareon is cheaper to get and would have STAB.

With larvitar candy so rare, I'd say to get someone else. Double dark would have solid attacking roles. As would one with a rock charge move.

For attack the dps difference between Bite/Stone Edge and Bite/Fireblast is pretty low. Defense I'd say it's a lot worse as water types counter Tyranitar meaning your charge move won't get STAB and will be resisted by common attackers.

It's kinda the worst charge move for offense and defense. Bite + SE / Crunch are much better attackers; and Iron Tail, Crunch, even Stone Edge are generally superior on defense. With Tyranitar, just spamming Bite would be better than most pokemon anyway -- so it doesn't matter too much.

Plus, as you said you can just stick him in a gym and work on the next one. That's what I would do.

Tyranitar falls in that awful group of pokemon that the developers have determined to have only one optimal useful move set. They put no thought into what moves a pokemon can get from what I can see. I'd just be glad you have the pokedex entry and just forget about him and use him as you feel appropriate. Niantic has made sure that your next evolve only has a 1/6 chance of being an ideal Tyranitar, it's sad but true. Edit I'm walking larvitar which is 97.8 ivs... but i'm sure when I evolve it I will be horribly disappointed, the randomness of this games always screws you in the end it seems.

Reroll. I got the same with my first one 98iv and got bite/SE on my second 95iv.

Bite/FB is the only bad moveset. Iron tail plus anything is good on defense

I see defensive movesets as speed bumps slowing people down when attacking gyms.
If your Tyranitar had the best defensive moveset, all that translates to is that it has a slightly higher speed bump than what it currently has.