Exhaust malfunction

So it's pretty simple, been playing a lot of support lately (or just taking exhaust on champs) and noticing a rather interesting trend against certain champs when I use exhaust on them. The attack speed and run speed slows are still applying as per usual, and before anything is said no none of the opponents had a QSS or Mercurial. Anyways, I've begun to notice that the attack damage reduction isn't necessarily applying. One game I was in as an azir, I went to 1v1 an Ashe she had a 100% crit ready flashed onto her and hit her with exhaust hit her with some soldiers and in that process she got a melee off while I was exhausted. I was crit for 1k (could've been 1,011 not recalling. Just know that I saw 4 digits on the crit icon). Me being rather baffled by this I had to conclude it was a 1,400-1,600 damage crit. But she only had an LW, boots, Phantom dancer, and Infinity Edge. So clearly her AD wasn't all that high. We get to end game and her highest crit was just above 1,400. If we do the math on that 1,400 x .4 = 560. 1400 - 560 = 840. But at the time of that game I'd assume she was only criting for around 1,000 or so. At that point it'd be a 600 damage crit. Needless to say I lost that duel before exhaust was up on her.

Case two, went against an AD malzhar as support lee. I went in got him down to like 40% before I was ult'd. I popped exhaust on him, and quickly died, I checked the recount damage. His pets had down over 1,400 damage to me. His pets are a part of his kit, so their damage should be lowered by the 40% as well. Seems a little off there.

And the last instance I can recall, was the same game. A rather tanky gnar came in at me with me at 200 health, mid hop in mega gnar I exhausted him and died soon after his landing. Recount said hop did 81 damage and he was the killer.

Can we take a look into the exhaust mechanic, because at this point I don't see a reason to take it unless I go against a kalista, and even then it only really hurts her early on when she has no attack speed so she can't jump/run away. I'd be better off with ignite on every support I play.

tl;dr Exhaust doesn't seem to apply the damage reduction from what I can see.