If you have high spellspeed and live on the east coast you're probably gonna clip. That's why I use a 0 Spellspeed build on all my Healers (2166 crit 1878 det atm). The job takes practice, just know that Malefic is there to weave in cards (which are less important now than ever; you can just toss them to random DPS tbh) and oGCD heals (which you should prioritize over GCD heals at every opportunity, to cast more Malefic). AST plays a lot like a shield healer, in that there's a large focus on using an ability now to deal with something later.

Your parse will be at least 30-40% (which is completely acceptable, though leaving something to be desired) if you simply maintain Combust/Malefic uptime, toss cards out randomly on cooldown, and align Divination properly.