Not finding DRK squishy at all.

[Reynhart]

When you reach level 51+ your stat weights are different, so you'll take more damage then someone level 50 in level 50 content until you're far enough that your Gear now provides the same mitigation.

Basically: Stat formulas are different for level 51+ characters so they end up taking more damage as a result.

Noted. I'll do further testing with two tanks at the exact same level.