Nah, a Dark type Pokémon, or just a Dark type move on any Pokémon, will take care of him. My Luxray finished basically the whole guy off with Crunch. Against his Bronzong, a fire move comes in handy though.
1. So, I dunno. You could do with almost anything. You should have a Ground type late in the game, and a dragon is always good. How about a Garchomp to cover these both? Dragon Claw/Outrage, if you can have one, Earthquake, Fire Fang and something else. Maybe Rock Climb if you want to include HMs.
2. Then you need a Surfer. Be sure to get a water Pokémon with good Sp. Atk. Or with good Atk., and then use Waterfall in battle instead of Surf. I always have a water Pokémon as a sort of a "HM slave", even though it's still a good battler. Those two with Strength and an ice type move to the fourth slot. Even my pretty low-level Empoleon's Blizzard took out Cynthia's Garchomp with one hit. That Garchomp is basically the only reason why you need ice. I think.
3. Next you ought to have a flyer. Drifblim is cool all-rounder and kind of a wall. As for moves, say, Fly, Shadow Ball, and you decide the rest. Toxic perhaps for slow stalling against neutral types. Possibly make it learn Psychic for additional coverage. Or Defog as a (useless) HM.
4. Steel type have good defences and resistances. All the better if it has Levitate, since that'll take care of ground moves, leaving it exposed to only fire. IMO this is better in the games than Heat Proof. So, a Bronzong is good, and I think Magnezone is even better. Have one with a nature that boosts Sp. Atk., and let it have Lock On, Thunder/Zap Cannon, Hyper Beam and Flash Cannon. >: ) (Heck, I should have a Magnezone like that on my next playthrough... Never actually had one.)
5. Have a Normal Pokémon like Blissey as your wall and healer. Also, Reflect, Light Screen, whatever, if you wish to use those. I have a Snorlax in SS but in an attacking role with Return. Return is a great move for any Normal type Pokémon if you keep it happy. Porygon-Z and Tauros are also cool. It wouldn't hurt to give these guys a fitting Grass type move, too, since I don't include a Grass type into this team suggestion. This Pokémon could also be your Cutter if you wanted it to be.
6. Have a Pokémon with Fighting type and Dark type moves to cover up even more opponents. Maybe a Lucario with Aura Sphere, Payback and a steel type move for STAB, too, if you wish. Rock Smash is an HM possibility.
Pretty much a perfect team IMO. I don't care if there are three steel types; I like steel types!

And only two of them are weak against fire and other too against ground. There are other Pokémon, though, more than capable of taking care of Fire and Ground type opponents. Besides, overusing one (good) type (like Steel) might come as a surprise even in competitive field. In the game, I don't care if they guys are weak against something if then can take it. And if then cannot, switch. Just ensuring there is a wide scale of moves to hit with is what I think is important. This party would have anything but a Rock and Bug move. And you can always teach your Normal type a Rock Slide if you want to, or U-Turn to some other.