We tested this issue in our reference environment today.
First, we looked at a video from the WoW Classic Beta, where the player was tanking Rhahk’zor in Deadmines at level 20:
https://www.reddit.com/r/classicwow/comments/br86ov/elite_damage_is_way_off_evidence/
If you look at his portrait while he’s getting hit, you can see him receiving 65-83 damage from Rhahk’zor. The average hit is ~75.
We then recreated it in the WoW Classic Beta-- a level 20 human warrior with similar gear, with Defensive Stance, and with Mark of the Wild. Here’s what that looked like:
We then did the same thing in our 1.12 reference environment. There, the test looked like this:
Conclusion: the average damage taken is identical.