I disagree with your points on TBN. It works now so it will work in EW. In ShB you use TBN if it will break. If it's not breaking, you aren't taking enough damage, so you can use % mitigation instead like Shadow Wall.

Giving DRK a regen (beyond Souleater) would not be balanced because TBN is very powerful and makes some content soloable the way self-heals allow on other tanks.

For OGCD aoe, DRK already has Flood of Shadow and many other aoe abilities, so it doesn't need the OGCD aoe the other tanks got.

Abyssal Drain is supposed to take health from each enemy, so it can heal you to full if there are lots of enemies.