Hey, Archy! I hope you don't mind if I chime in. I may not be the most knowledgeable, but after battling your team a couple times, I think I have an idea on what could help.
Your Heatran is interesting. It's running EVs for an offensive set, yet having Stealth Rocks at the same time. Not that they can't go together, but I think that your team would benefit from having a more defensively based member. You know, something to take a couple hits and set up your other sweepers for success.
Heatran @ Leftovers
Ability: Flash Fire
EVs: 248 HP / 192 SpD / 68 Spe
Calm Nature
- Lava Plume
- Toxic
- Taunt/Flash Cannon
- Stealth Rock
This is so you can get Stealth Rocks out consistently, while also being able to handle fast special attackers. Taunt is normally run here, but since I know you like offensive power, I think Flash Cannon would work as well. Choice Scarf Heatran is also an option, if you're looking for a bulky special attacker, but you would lose the Stealth Rocks, but I'll get to that later.
Heatran @ Choice Scarf
Ability: Flash Fire
EVs: 28 HP / 252 SpA / 228 Spe
Timid Nature
- Overheat
- Flash Cannon
- Earth Power
- Stone Edge
It packs a punch, and is very fast right out of the gate. Since you would be losing your Stealth Rocks setter, Clefable might make a good replacement since you said Serperior wasn't really pulling its weight.
Clefable @ Leftovers
Ability: Magic Guard
EVs: 252 HP / 172 Def / 84 SpD
Calm Nature
- Stealth Rock
- Moonblast
- Thunder Wave
- Soft-Boiled
Thunder Wave would help a lot against some set up sweepers that would normally threaten your team. Clefable also makes a very good status absorber alongside Starmie, which would be great for protecting your main damage dealers.
If you want to keep Heatran the same, then I would suggest switching Serperior for Sableye. It's great for making physical threats absolutely worthless, and is just a general nuisance.
Sableye @ Leftovers
Ability: Prankster
EVs: 252 HP / 112 Def / 144 SpD
Careful Nature
- Knock Off
- Will-O-Wisp
- Recover
- Foul Play/Toxic
This set brings in a lot of utility. It may seem weird at first to include Will-O-Wisp and Toxic in the same set, but they compliment each other quite well, especially when opposing Talonflame want to switch in and set up. Foul Play works too so Sableye isn't complete Taunt bait or set-up fodder.
I know you don't like defensive pokemon, but I believe that they're necessary in every team, even hyper offense. Since if every pokemon is a potent sweeper, who's going to take those status ailments, or weaken the opposing team's walls when they can't be OHKO'd? Right now, you're wrecked by Choice Scarf sweepers, since besides Ice Shard, you can't touch them. Just a few thoughts I had after our battles.