Tank Mitigation vs Tank DPS.

[Ultimatecalibur]

If you clear fights faster because of damage output, meaning less healing overall, it is logical what stat should be most desired.

Not really. The key factor is how significant the increase is. A 2.7% increase in a tank's damage when they are expected to provide 10% of the total damage done to the boss only shortens a 10 minute fight by about 17 seconds. On the other hand, increasing mitigation and self healing by 8% might mean that a tank feels significantly less squishy allowing a healer to comfortably dps more.