Rhydon worth it?

I turned my MS/E Rhydon into a defender because I really didn't use him as an attacker. Against fire and electric, if I even see them, I use my Sandslash (or Vaporeon against fire.) As a defender it isn't any worse than any other high cp defender with a double weakness. I would certainly stick that in a gym that doesn't have a Rhydon in it. It isn't the ideal defending moveset, and EQ is now pretty easy to dodge, but he still isn't much worse than most other defenders you can stick in there.

This is good advice -- plus in the current meta CP is king and 95% Rhydon won't be surpassed by many Pokémon.

Movesets are more important. A move set that's 90% as effective will be exactly that, 90% as effective. But something with 90%IVs (and the same moves) will be roughly 98% as effective as something with perfect IVs. In the latter case, you're just talking about how close you are to "perfection" in the additional 15IV points per category you can get, which are relatively small compared to the base stats.