Personally I've given up hopes on a parser, doubly so as a ps4 player.

On subject, overall an AST will have trouble DPSing comparable to the other healers, thus getting the most out of your cards help bridge that gap. You are right an AST can clear content without maximizing the deck but doing so helps out your party more, think along the lines of a high SCH DPS. Since we have no parcer when it comes to this an AST must be observant, seeing how often effects go out, how quickly single targets go down compared to a group and, player tendencies toward mechanics as well as the RNG of cards themselves.

Of course this is all up to the player, and it can be a bit of work especially in the middle of a fight but at least trying might make that dungeon run a little easier, or give you a little breathing room for enrage timers.