@DragonFireKai
Blizzard has made it fairly clear that they want the melee DPS specs to do the interrupts and not the tanks. Yes, there are tanks that "have a reliable interrupt" using your definitions, but having DPS do it was the reason retribution was given it as the talented ability Rebuke instead of it being moved baseline for paladins. Between rogues, shaman, feral druids, warriors, dks, ret pallies, and I think even hunters that if the tank has to be the one worrying about interrupts that you need to fire your DPS and recruit new ones. Yes, it's nice to have additional toys, but there are 4-39 other people who can possibly provide them depending on what level of PvE you're playing.

The AP/AS debuffs, I really don't care at the moment. I'm not going to be facing 7-10 trash mobs at once anymore except in rare occasions. We've got one of the more reliable blocks in the game and can take the punishment. On boss fights, it's rare for a single tank to be grabbing multiple bosses at once, so being able to hit multiple bosses with those debuffs is also not much to worry about.

DKs were the tanks they were in T7 and T8 because they weren't balanced at all. Their number of cooldowns was fine, but the cooldowns weren't balanced to begin with. At that time you could run 5 level appropriate blood specced DKs through BC dungeons without needing a healer. However, yes, the primary reason these overpowered cooldowns were so effective was the massive boss damage mechanics you mentioned. The reason for these massive damage mechanics were that healers virtually couldn't run out of mana. They had to make the healers cast as much as possible, because managing mana was a joke.

In Cataclysm, the healing game is changing which also means the boss damage mechanics are also going to be changing. We're not going to see the exact same type of damage components in boss fights, because A) the healers would run out of mana. B) everyone has more health than they used to. C) bosses (in normal modes) will be hitting for less so that the time between alive and dead is no longer 1 healing GCD. We should be able to take 5-10 hits before dying instead of the 2 it is now.

All in all, I don't care what someone else's toolbox looks like. I just care that mine works and does the job it needs to do.