There are a few ways good DPS can "carry" a tank.. lets see.
They can use proper CC both before the pull and during (such as stuns), put up proper damage reducing debuffs, interrupt spell casts (HUGE), move out of bad (to help the healer), make sure to not pull threat, consistently using threat re-directing abilities, not pulling more then the minimum number of creatures, tossing out off healing if needed, tanking or kiting creatures briefly if needed.
Those are not carrying. Those are how you are supposed to play. I know, it's crazy, the thought that DPS would do anything other than mindlessly punch something. But here's the reality:
This gets its own line.
If you're not using all your abilities, you or someone else is overgeared and there is carrying going on.
Or to put it another way:
DPS have gotten so damn spoiled by tanks carrying them that the moment the tank puts them down, the DPS thinks they are carrying the tank.
Or to put it another another way:
This is part of why I got sick of WoW. I like the idea of tanking, but the actual practice of it is a pain in the ass because so many people play like absolute shit and then whine that it's my fault.
Most DPS aren't bad. Most players aren't bad. But the players who are bad are noticeable.
It is possible to carry a tank, in extreme circumstances. If we assume that the healer is properly geared and skilled, but still cannot keep up the tank, then a DPS helping with heals will be carrying the tank. Similarly, if the healer is overgeared, they may be carrying the tank. But...
Using CC and interrupts are not at all carrying the tank. They're your fucking job. Fuck. You've got me swearing about how fucking stupid you are being. You know who you are. Fuckers.
I think I just used more bold text in this post than I have this entire year, and the one before. God dammit.
Oh here, masterlooter had a pretty good comment, slightly trimmed.
I think there might be a confusion on terminology here.
"Carrying" implies that the group/raid could very likely have done the event without the "carried" player being there at all.If you're saying that you're "carrying" a tank. that means you could have done the instance without a tank altogether.
Other players needing to CC, interupt, "heal more", and aggro dump are NOT indicators of "carrying" a tank. It's just using different strategies with the group you have at hand. It's no different than how some guilds 2 tank Omnitron, and others single tank it. Those with 2 tanks are not "carrying" another tank - just using a different strategy.
Four man a heroic 5 man instance without someone in a tank spec, then you can say you're able to "carry" a tank.
On a lighter note, tomorrow I will complain about Nazis.