In the video below you see a lvl 38 Prot Paladin getting hit by Quillboar Champions for max 54 Damage
https://youtu.be/a6x-XtiMclQ?t=3807
I went in there as a lvl 39 Prot Paladin and their normal hits do 160-200 damage each hit with frequent crits that do 300+ damage. With 195 defense in Classic i would be crit immune to lvl 31 mobs.
I think this is a bug. If not, and the justification is increased player power, i don't see a 3-4x multiplier in player power or hp. Tanking needs some incentive, if you are not able to do fun stuff like slowly soloing dungeons that are populated by grey mobs it is no wonder nobody wants to tank.