Gyarados with B/OR... Worth power up?

I would wait for a better one with dragon tail

I am assuming you are looking for a Dragonite attacker and if that’s the case then yes, this is a good moveset. The only thing better would be a DB/DP legacy moveset (these wreck my Dragonites when they are on Def). Bite gives you the ability to dodge and OR is a good move against Dragonite. Just as a side note, I would only power him up until you really need him as an attacker. I usually do not fully pump up attackers, especially ones with fast quick moves that I know I will be dodging with anyway, because attacking gyms in this game is a joke and you don’t need a 3000 cp mon to attack anything.

I don't like my B/OR Gary for attacking. Might be okay against Dragonite, but there are other pokemon I like better for that task.

Yea nvm screw your hard work start grinding boy