I did a monorun on Ruby once back in 2009 with a Whismur, so I pretty much only had an Exploud at level 50s against the Elite Four.
Surprisingly enough, it wasn't difficult at all. With the right moveset and LOTS of items, the E4 is a cakewalk, and even a less than decent Pokemon like Exploud can steamroll the E4 with no problem. The only problem was Steven, but Earthquake pretty much dealt with every Pokemon except Skarmory. Screw Skarmory.
I didn't even use hyper beam. The only STAB move I had was Return.