100% IV but...

On gym defense, just because it is 100% IV, and Megahorn, though sub-optimal, still quite useful in some match-ups.

I feel you man. I have two of them. Hoping with Rhyperior they will get better moves.
Just save them as is.

My condolences

Its high CP will sit high in gyms if you max it out, then you'll hopefully roll a better moveset when Rhyperior becomes a thing (assuming movesets still work the same by that point). No harm in powering it up I'd say, if you can spare the dust

Like others have said it's gym placement will be favorable. If Niantic changes gym placement such that cp is not the determine factor, then that advantage will be obsolete.

If Super Effectiveness is ever increased (by Niantic) such that Super Effective > STAB, this moveset will have much more merit (in PvP, unfortunately in the current gym situation where defenders are static {they don't switch out} a moveset of the same typing is much more useful, or at least with two stab moves at the moment)

Go for it my friend. It's 100%, don't waste it

I have a 87% that i maxed with the same moveset because both those moves are good for defence

I would only power it up if you have extra candies and dust to burn. Save it until they introduce rerolls of movesets or maybe Rock Smash or Megahorn get buffed.

If you need a high level CP mon that sits high in gyms I guess he would be good for that. But he's not really good at all with that moveset.

with 4th generation he will evolve and get new moves so now orries and put candies into him