Skill would be equal gear, no addons or identical addons, on equally powerful systems with the same latency.
Pretty much only the Blizzard professional tournament thing.

Once you outgear someone else, you have an advantage and need less skill to win.
If you outnumber the other guys, that's less skill too.

Not saying one cannot be very skillful, despite having advantages.

I've seen videos where someone wipes large groups of opposition, in their Captain or Generals room.
But they were not subject to many Frost Nova / Ring of Frosts, nor were they hit with Fear several times, nor were their toons Frost Trapped or Polymorphed, etc.
When I'm subject to those kind of effects, there's no chance of wiping 12 Horde at Belinda; but when they ignore me or only use hit point damage against me, 20 horde are rather easy to kill in the same place.



@Sam:
I've got close to 30,000 HK's, on my Pally/DK's team.
When any member kills someone, they all get the HK.

The only thing that wouldn't transfer across to everyone, would be kills or killing blows... assuming that is tracked on the statistics page.