Having to reserve Spread for Spear to shorten Luminiferous Aether CD is just silly. It basically doesn't allow for any rng control over other buffs, making AST completely unreliable as a buffer.
A lot of skills need to be fixed, anyone saying otherwise have no clue how powerful SCH and WHM are with post LV 50 skills. Also MP management is a real issue. I reach the end of the new dungeons with full MP with my SCH while also doing dps, with AST I have to use Lum. Aeth. every time it's available and I cannot DPS unless the party is decent and can dodge aoes.
I'm not saying AST in useless of course, it's simply less efficient than the other to healers in every possible way.