There seems to be a lot of issues if AST becomes a little-to-no direct DPS usage job. The problem is what kind of GCD support tool can outweigh a Malefic spam? The nature of the game makes DPS > most general support toolkits unless support skill is a DPS buff. Having it tied to the GCD means it has to be fairly spammable, and too strong of an effect will break game balance and make malefic not worth casting. It sounds good in theory but not feasible to implement. oGCD support tools have an innate advantage in that they can be weaved into a combo so even if a support tool doesn't give a DPS buff, it's still a beneficial utility. GCDs on the other hand aren't.
The real reason healers DPS is to maximize and optimize the efficiency of their toolkit and contribution to its max. This is especially the case for savage level raids. However... pure healers who don't want to DPS means they do not have the mindset of optimizing their toolkit for max contribution, which also means they won't be doing difficult content that requires mandatory DPS. If anything they'll be doing normal content and 4-man content, which would be counter productive to what rDPS is aimed for.
The second issue is gameplay progression. The effect of rDPS varys greatly depending on the number of players in a party - If the AST (with little-to-no DPS Usage but has rDPS skills) doing 4-man content, they are essentially only able to achieve less than half as much potential from their toolkit than the other healers's toolkits (as their main source of damage is composed of 3 people and not 7). For MSQ storyline content and solo instances / with just a Chocobo, they'll be down to 2 (and technically less than 2 because rDPS is boosting only a small portion of your Chocobo's DPS). This effectively locks them into a raid-healer-only job category. At that point, their actual DPS skills in the open world is their Malefic + Combust spam, which ultimately just changes nothing for variety. That's a big reason why I preferred Lord of Crowns minor arcana to keep the flat attack potency rather than exchange it for an 4 - 8% boost.
The third issue is balance with other healers. rDPS scaling from 3 players to 7 players will inevitably break balance.
There's no way to truly a good way to make a healer not "DPS" but still contribute to DPS fairly without ruining some form of gameplay somewhere else. SE already tried to delete DPS to make it easier for healers... but you know how bad that went. The real solution is really to just encourage DPSing for a healer.