Are you serious? I mean, for real? I know warriors are OP, and they are the clear number 1 choise, but despite that, DK's are *incredible* for solo tanking garrosh. Few things you might not be considering -
DK's have more cooldowns to match the stacks, along with anti magic shell for every whirl+stack explosion, essentially absorbing the "Big hit" and the whirl at the same time.
DK's can keep themselves alive for longer periods of time, allowing healers etc to deal with their adds rather than focus on the tank.
DK's survivability (death strike) scales with the damage intake - but it doesn't work on magic damage. What this means is that you get an *extremely* smooth damage curve. You'll sit at 500K vengeance, having your DS basicly shield you for more than half your healthpool and heal you up, counteracting all the physical "spike" hits - leaving all the damage intake from the DoT that's constantly ticking.
As for DPS,
http://www.warcraftlogs.com/reports/...pe=damage-done this was our second kill, and our first solo-tanked kill (prot warr was absent so we had to improvise).
Few things you might want to consider when looking at the log and comparing it to those above me -
We use the AFK terrace tactic (1 minute of zero dmg).
I don't stand in annihilates (no reason to stress the healers when we end up waiting later on anyway).
I don't "whore vengeance" in any way, really.