Gyrados Waterfall?

I am not sure why you TMed bite/crunch unless you have several. They are useful against focus blast MewTwo.

I did TM a DragonTail/ hydropump. My pile on question is whether this combination is powerful enough to justify powering up a lower level Gyarados with Waterfall//hydropump to level 30. Do they outperform the higher level vaporeons I already have?

I hope you used a charge TM too because Waterfall/Crunch has absolutely no use as a moveset.

I'm making myself a Water and a Dark gyarados using TMs and in the future i'll see what i need. I have a mewtwo to battle 12
/18. maybe i will tm one more and turn it back to its original moveset. but i will not touch the Dragon Tail ones i have 6 gyarados from level 25 to 35

I would at least keep one gyarados with bite + hydro pump, gyarados' mega evolution becomes a water / dark hybrid

I have zero reason to save Bite. Gyarados with Dark moves severely lags more optimal counters against Psychic, including Tyranitar, Houndoom, Scizor, Dragonite of various movesets, Mewtwo itself, Raikou, and Gyarados WITH Waterfall. Pokebattler lists my B/C Gary as my 13th best counter in time to win and 16th overall. Even against Focus Blast, it's only the sixth best counter. Against Alakazam, it's 9th and 8th, respectively; i.e., not good enough. TM it.