It really depends on how you look at AST.

If you look at AST through the lens of just being a healer, it's significantly behind the other two jobs. Not enough that it can't do content, but it's harder and less forgiving on AST. And Alex Savage really rather requires you look at healers as healers.

If you look at AST from angles like support/buffer/utility/etc, it's not so bad. But some content doesn't let you do that.