Thunderpunch is unnecessary because although it would do well against water and flying, an icepunch would include more pokemon that could easily get me super effective hits (namely dragon types!), which is already unnecessary because of reversal, and endure, when carried out successfully,will have a base power of 200, which will easily do it's toll on ALMOST every water and flying type out there, and every other type combo too, unless of course they happen be ghost type, which is why I have zen headbutt. The other problem was speed, medicham has base 80 speed (not too shabby, but leaves huge room for error), but with one stage due to salac berry, this base value is multiplied by 1.5, and ends up at 120, which is faster than most pokemon go. This means that once it gets going, it will be hard to stop, unless you use something like quick attack. So if Im at 1 hp, with this a buffered up reversal at my disposal, but I can see an obvious quick attack/bullet punch coming, it may be useful to also use something like quick attack.

The catch- the only damaging first priority move medicham can get is vacuum wave, which is special and won't take advantage of pure power.
So I was wondering if anyone here knows a move that will fix this dilemma.

I thought of that, but it won't get me to the exactness I need to be at.

hmm im out of ideas if you don't wanna start over. ;w;

Medicham can still be used like that though. You'll just need to scout out which pokemon of theres have first priority moves and ko em with another member of your team. They're usually pretty obvious who has them, Metagross, scizor, hitmontop. Wish I could be more help but thats all i got. .-.