Let me start by saying that I love Poliwrath as a defender. He is a solid and annoying defender to deal with. Unfortunately, he likely is no longer a relevant defender for most gym areas now because of Poliwrath's such low CP. He/She will always sit in the bottom and will be kicked out first. So, I would advise against powering up your wrath unless your gym meta area has extremely low CP ranges, that Poliwrath would be viable to stay in gyms.
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Poliwrath decision
So i never find any good IV poliwags and dont hatch many often either but during the water event i finally caught one worth evolving to poliwrath, 87% IV (14/11/14) with rock smash and ice punch which has an A-rated defending moveset on here, my last decent IV poliwrath rolled a bad moveset (mudshot/sub) so should i power this one up to at least level 30 if not higher to be a defender? Or just leave it where it is as a prestiger and try to get a better one? which for me has not been easy