So yeah, I not only tried him, I tried him in an extremely favorable environment since only running 3 Pokemon that game gave him higher levels than he normally would have had.
Sounds like you just had bad luck with it.
Like i said before, Dwebble owns the 4th, 6th, 7th, and 8th gym. It destroys 3/4 of the E4 (possibly one of the best pokes for the end game boss battles). And it destroys Ghetsis too.
Vs the 4th gym: Smack Down/Rock Tomb puts a quick stop to Emolga's, and Dig makes short work of Zebstrika.
Vs the 6th gym: It's a rock type vs flying type. Whatdya expect other than quick ownage?
Vs the 7th gym: Just use Shell Smash and kill everything With X-Scissor. You might need Rock Slide for Beartic tho, idk.
Vs the 8th gym: Shell Smash against Fraxure, it'll use Dragon Dance. Then, kill it with Rock Slide. When Druddigon comes out, use Shell Smash or Rock Slide. Rock Slide Haxorus, then it's gg.
Vs: Grimsley: Stay away from Scrafty, then once Scrafty is gone, set up Shell Smash, and X-Scissor everything else.
Vs Caitlin: Shell Smash, survive Psychic due to Sturdy, then kill everything with X-Scissor, be sure to use X-Scissor on Sigilyph and not Rock Slide, cuz Rock Slide might miss, and X-Scissor kills it anyway.
Vs Shauntal: Shell Smash, Rawst Berry off the Burn, Shadow Claw, Confarigus is gone, and you still got full HP, and Shell Smash. Kill all else with Shadow Claw, and Rock Slide the candle thing.
Vs Ghetsis: Substitute on Confarigus, Shell Smash 3 times, win.
Sounds like High tier to me.