Tank Mitigation vs Tank DPS.

[Taika]

And it does make difference, could affect the whole party performance with a healer being able to dish out one dps move. Its like a healer having additional extra 1400 spell speed reducing his gcd by 0.12 sec.
This is enough to make up for that 1-2% damage difference on a tank.
The thing becomes even more obvious in dungeons, where there is a constant source of high damage hitting a tank.

Please trust the healers when they say that whatever the tank has or hasn't melded won't affect their healing ability use in any content. What makes a difference is item level (defense and HP) and use of cooldowns. The healer will not be healing any more or less if their tank has full tenacity melds, full direct hit melds, or no melds at all, if the playstyle is otherwise the same.