Poliwrath with submission as good as hydro pump? Need some pro help!

I think the general consensus is all 3 are good on defense. It's really all about Bubble.

My personal favorite to put on defense is Ice Punch b/c it covers almost every one of his weaknesses. Could throw an attacker off rolling in with a grass type, or Dragonite especially.

But none of them are bad. They're just different. One might trick one person, one might get another. But at the end of the day if someone really wants that gym they'll take it. So don't overthink it and pick the one with the highest IV's ;)

Bubble + Submission is the best in gym defense
Mud Shot + Hydro Pump is the best in attacking gym

Submission (despite having STAB) is bad against Poison and Psychic, which are the most common second types of Grass attackers.

Ice Punch is awesome on this guy (as a defense move, obviously), cause you can actually do something against Dragonites and Grass attackers.

Hydro Pump is a little bit better imo, because the damage is huge anyway and you can use your Poliwrath (if it has Bubble too) for both attack and gym defense ^^