Bio II is instant now, and loss of Aero is meh. You still have Miasma II (also instant). Shadow Flare is also instant. You lose some offense in favor of maneuverability, which a SCH should have probably more than any other healer.

Everyone knew this was coming. The devs themselves stated that they felt SCH was too powerful. The loss of sustain is also to put SCH in check.

As for AST 900 potency heal, each healer has been given something to compete with this. I need remind you that lustrate potency has increased, and pac-manning your fairy is highly unused. The tether is really interesting. You know Anchag, the first boss in Amdapor Keep hard where the player tethered is hit for high damage at a really high rate and has to duck behind a statue? It is basically the same thing except it heals.

Is there a reason to not go AST now? I don't know. Is there? This expansion is going to come out, people will play and adjustments will be made in future patches. Whether or not you're an AST at this point, I guess we will see.