As far as CU vs Asylum goes, you cast CU it plants a HoT on anyone who enters and the hot stays on the target for the entire duration even if CU is cancelled. Everyone has to stay in asylum the entire time to get heals, which doesn't happen a lot of the time.

ED vs Tetra, you know that ED was always better right? If you were at low HP it would have a power level of 1000 instead of a flat 700, it was something that was actually pretty nice and different.

Here is the question though. If you had a choice
*A class that buffs other players and makes the fight end faster, has a better raid oh crap moment cooldown on the move, and casts faster and has a lower GCD
*A class that provides around ~3% more healing and nothing else really.

IMO they really should have pushed AST's class identity to be even faster but still had those weaker heals to average it out while pushing WHM in a different direction like giving temporary HP buffs which stacks with other's DR abilities.