Actually I'm assuming I have Stealth Rock up (yes, I'm still running stealth rock on my Mesprit / Uxie ... currently Mesprit), in which case none of the sashed or sturdy pokemon are a problem assuming Stealth Rock is up, and actually I forgot to factor in stealth rock damage for those 4x resists (I think all Heatran are almost guaranteed 2HKO factoring in Stealth Rock?). But yah, quite a few things still beat Metagross.
I was using Mesprit / Metagross / Suicune (Suicune takes care of nearly everything that Metagross can't), but every time lost because Metagross or Suicune wasn't able to fully set up. Never lost when fully set up so far.
Also, Dragon Tail is NOT exactly same as roar. Under a sub, Dragon Tail only deals damage.
Apart from Tinted Lens, the main problem with Volcarona is that Bug Buzz is a sound move, which means it is potentially totally walled by Sound Proof pokemon (Venomoth can Signal Beam for 75 base power, whereas Volcarona can just use Silver Wind, which doesn't have enough PP for things like Pressure Moltres, and of course the base power is too low). That's why my Volcarona just runs Flamethrower + HP Rock, with no recovery move.
Yeah, 110 base speed is sometimes not fast enough anymore. Things just need to be extremely bulky like Registeel / Suicune / Snorlax or have a speed boosting move to be more reliable it seems.
A while ago I was thinking about using a defensive calm mind Cobalion (91/129 Defense is impressive enough I figured)... something like Calm Mind / Sub / Flash Cannon / HP Fighting... never got around to catching such Cobalion... I dunno. I imagine it'd do well enough, but 72 Sp Def might still be a bit troublesome.
All that said, I'm thinking I might just take a break from Single and have some fun in Double.