When I did my dungeons I went as tank since was faster queues I was getting often 2-3 commendations. And all I did was trying to finish them the fastest way according to player lvl and jobs. If I had a low lvl healer I had to do split pulls or several splits if 2 or 2 DD were low too. Of course being polite and giving instructions if need so they expect what i will do.
Is like, you go to DF and you get a healer lvl 110 then 1 bard and 1 blm lvl 110+ what you expect to do? Slow? Of course not, right? Even If you get a ranged and 1 melee high speed runs is still possible as long healer is high to keep up with heals and dps to finish them fast to not burden both tank and healer. Now if I get 2 melees even being high I do small packs since is better that and I will still finish as if was speed run.
About telling tanks being bad they got a good solution, go tank yourselves. You don't want? Then deal with it... Simple.