Good post.
1.) I'll emphasize your point you made in Dipping that: enemies should have access to the same standard abilities as us (obviously not our class-/race-specific abilities). If we can dip, the AI should dip. If we can jump to disengage, the enemy should be able to.
2.) Your fix to backstabbing is too complex imo. At the very least, it shouldn't provoke AoO and allow a save by the enemy for half damage. That is too punishing for the player. I suggest either:
-flanking (require ally on other side of enemy for Advantage). This adds some level of tactics/cost while preserving the ability to get Advantage
-OR flat, smaller bonus (+2) to hit. This reduces the bonus you get for freely circling around. (This is what Topgoon suggested)
-OR provokes AoO to get behind an enemy. This increases the cost (get AoO's or use disengage jump) to get such a powerful Advantage
