Kingdra, water or dragon attacker?

Im sure you have a high level Vaporeon army which is a better water attacker...so a Dragon attacker would be more useful against Dragonites.

I've been trying to get DB&B on once cas he's one of my favorite mons and it would be fun as a dragonite attacker, but in reality it's a subpar attacker for both types there's better mons to choose from. Outrage makes it too easy to get hit from a dragonite. If u wanna use it as a dragonite attacker I think DB&Blizzard is probably better then DB&O

If you want to make it relevant, double water moves against a certain legendary burning chicken comes to mind...

Though a water attacker would be better for raids, you probably already have plenty of Vaporeons that are better. You would also risk getting blizzard if you try to go that way.
Going Dragon would make him a good generalist attacker or decent defender, if gyms ever become a challenge again.
All said, you probably have better spots to use a TM based on the current meta.

P.S. I was in a similar situation. I wanted to make one relevant and took a stab it. It was DB/B. I used a charge TM. If I drew HP I was going to use a fast TM to make it good for fire types. But I drew Outrage and decided it wasn't worth any more resources. Maybe my next one with be my water one...

I would like to keep this move or change to DB + Hydro Pump

fast tm's are easier to come by, and you could roll blizzard with a charge. with dragon movesets and a double resistance to water makes him a good attacker against water.

I don't see the point without prestige in a Dragon based Kingdra.

It will do extra damage, and take extra damage from a dragonite. No thanks, I got plenty of Ice Pokemon, or stronger Dragonites for that.

It's got a double resistance to fire, so like Omy, it becomes a less potion intensive investment than Vaperon.

This is what I miss most about prestiging. Tons of pokemon that had use in prestige game, don't really have as much in raid game.

Go for WG/Hydro IMO. And use it to save potions vs fire.

The other option is to use a DB/O Kingdra against water types (with water moves). This is similar to using a grass against water, accept the dmg you deal and receive is halved, making for a slow and steady battle. I think DB/O being such a good/fun moveset makes this a viable option.