While you've proven pretty handily that you're not willing to be swayed by the logic of others, I still feel compelled to pull apart the fight a little further, and prove that your hypothetical scenario doesn't actually exist.
Warning: Rough numbers ahead.
On Wind Lord, the boss has 270mil health, 10 man normal - each of the adds has 50 mil hp, damage is spread between the three adds of a certain subgroup.
420 mil damage needs to go out in 8 minutes. 875,000 raid DPS - usually split between 1 tank, 6 DPS, 3 healers. If the tank was doing minimal damage throughout this fight the DPS requirement for all those DPS would be somewhere around 140k.
Not bad, a lot of classes can pull some pretty sick cleave DPS on that fight, and there is the massive damage bonus you get in the final phase - but what about those who can't cleave? Or people without strong burn phase cooldowns? I doubt you care, because honestly you seem a little selfish, and you play a warlock, but some specs would be benched on Wind Lord because they simply can't really hack these strange mechanics.
Or more likely - it was anticipated that tanks would be doing huge damage on this fight - hence the strict enrage timer. Factoring in the tank as a functional DPS on this fight, the damage requirement to beat the enrage drops to 125k dps, which is much more manageable. Cleave specs will still over perform, and poor cleavers will still underperform that number a little, but the relaxed requirement enables those specs to be less detrimental.
In short - tank DPS was factored into this encounter's enrage timer, and DPS still needs to perform their role optimally. DPS are still required to perform well. They are still necessary. There is no problem here. None.
It's worth noting while you examine these numbers that normal modes are tuned to the expectation that people are wearing a mix of blues and epics, item levels much lower than we see today. The fight done properly might have even required two tanks to split the adds, for some groups - making the enrage timer even tighter.