I mean, technically, what's also being suggested is not like AST, because AST cards are oGCD. While, Mercy has to choose to Heal beam, Damage Beam or use her pistol for personal damage (But 99.99% of the time, you'll be just holding M1 with Heal Beam. Due to the nature of FPS games where your target's always going to be taking some damage... Also, unlike say, Ana whom burst heals like crazy so can afford to pot shot enemies for damage, Mercy's healing beam is slow, continuous healing. Hence why she's terribly designed. She's just a trash version of TF2's Medic whom at least had overhealing building up additional health beyond 100% which was critical for screwing with Snipers)

Meaning that the suggestion would be more akin to having GCD actions that buffed damage of others. As an alternative to pressing DPS buttons. This could come in the form of buffs and debuffs.

It is an interesting position, wherein it can create some interesting gameplay between periods of healing, which doesn't rely on having to have a complex personal damage rotation.

It however, is a long shot, because:

DaNcEr Is BuFfEr

Like, everything about buffs in ShB comes down to that statement. Nerf SCH's Chain Stratagem. Gut AST's cards. Continue to not give WHM a single buff (Despite White Magic traditionally being where literally all the Buffs in the FF series have been, from Berserk to Haste to Bravery to Faith and more). Why? Because Dancer.

Ignoring the fact that Dancer has all of 3 buffs... DMG up for Partner, Crit up for Partner and DMG up for Party...

All the while, you can easily make part of healer tDPS being that they can exploit weaknesses in the enemy or embolden their allies. Having SCH apply debilitating poisons and toxins as well as using skills like Libra. Have AST have a card system that isn't RNG and isn't neutered down into "All Card Make Damage Gooder". WHM can get some of the temporary buffs that are classic to the franchise.

This need not only stop at rDPS buffs either, you can also make healing somewhat about providing utility and defensive buffs. Who wouldn't like to see Protect and Shell being variants of Palisade and Apocatastasis respectively? Having Nul/Bar skills? Float? Gain-spells?

To say nothing about utility based debuff skills like Dispel, Blind, Slow, Fog or even Sap if they thought of a way to make it functional for the games combat system...

All this, could be an alternative to the upcoming 1 Nuke, 1 DoT, 1 AoE as a way to fill time between heals.

But no, because Dancer...