Remove (or drastically lower) the Damage & Healing Bonuses From Expertise
This would have a few consequences. First, reducing damage done increases TTK, and reducing healing done prevents this change from making healers god-like. Each player would have more survivability on their own, which would allow everyone to stay in the fight longer. Second, that means expertise has less of an effect on someone's performance, which would help to reduce the gear gap. These are two of the most common complaints I see, and this change would solve both.
(If There Were a Second Change I'd Make...)
It would be to the new resolve; the intent was actually a good one. A PuG can never coordinate CC like a premade on voice chat can, and it is clear the change to resolve was meant to reduce this discrepancy. I'm in favor of that, but it went too far; I think applying CC to a target that is already CC'd should maybe count for half the resolve it would normally incur.