Offensive Volcarona can OHKO Haxorus with bug buzz after a QD (and even with no boosts when using LO) so that's a minor point. As for DNite: beware as it can do up to 47% with a CB extremespeed and the dragon dance variant can easily set up on you and then 2hko (considering the turn needed to break the sub) with dragon claw.
Why would you compare my set with offensive Rona?
I am using the exact same set as the defensive morning sun Volcarona except that i use sub over a Fire move and i have put 24 evs in speed to outspeed base 115s at +1.
So if you compare it with it you see how this set can easily deal with CB dragons while the normal cant.
About the ES comment.Since i am won't be bringing Volcarona in on a Dragonite we are assuming that he comes in after i force something out right?
So if he does that then i am fine 'cause i will already be behind a sub and i can heal 66% of my life at will so no problem.
Finally offensive Dnite will never get a chance to kill me since i will be faster and behind a sub.So let's assume i use QD on the switch i force and then he comes in and uses DD as i sub up.Now if he doesn't break the sub i will go at +/6+/6+6/ and wait to eventually burn him.
If dnite uses Outrage it will lose from confusion and Burn damage eventually.If it uses Dragon Claw,then after i Burn it i will switch into my physical wall to handle him.
For example in the worse situation that could happen,meaning adamant dnite with Life Orb,Gliscor can still wall him taking:
1612 Atk vs 365 Def & 354 HP (80 Base Power): 247 - 292 (69.77% - 82.49%)
I know that it sounds too much but note that Life Orb is almost never seen with Dragon Claw.Life Orb is almost always paired with Outrage for brute power and generally Life Orb is no the preferred item on a Dnite(even on an offensive one).
Lum Berry and Lefties are the best items and when Dnite holds them it does to gliscor with Dragon Claw burned at +6 :
1612 Atk vs 365 Def & 354 HP (80 Base Power): 190 - 225 (53.67% - 63.56%)