The MOB level in missions was announced "fixed". I've not noticed a single change, either at level 62 or at level 18 (the levels at which I most often play). At both levels, a mission 1 click down from 50% yields a mission 100% full of no-xp grey mobs.

L62, 49%: 95% grey, 5% min. green
L18, 49%: 100% grey
L62, 50%: 95% min. green, 1 or 2 yellow or +1 orange
L18, 50%: 30% high green, 40% even, 20% +1 orange, 10% +2 orange

This is zero change from 13.1. IMHO, a 50% mission should be nearly 100% even con yellow with 1 or 2 -1/+1 MOBs and there should not be such a huge difference between 49% and 50%. You might as well just lop off the lower half of the mission slider.

Tighten up the range on MOBs to +1/-1 of the mission QL. Give a MOB an automatic -1 for each additional MOB in the same room. If you want to ****e it up, on rare occasion, generate one +2 MOB and make sure he's packing something.