Two Healers together in well coordinated, zero mistake perfect runs heal through oGCD rotations. Important distinction.
And no, Healers do not "need" a DPS rotation.
Tanks and DPS need only watch out for mechanics while doing their rotations. Healers need to monitor the party status while also watching for mechanics and you want to add full blown DPS rotations into that?
If you want to play a job that does damage and sometimes heals, Theres a job called Red Mage that sounds right up your alley.
What Healers need is for Damage to not compete with Healing. Take Glare/Broil/Malefic off the GCD with a 1~2 second cooldown (AoEs would trigger that cooldown to prevent them being used as DPS GCD fillers).
Fill empty GCDs with Cures. 2x Cure is more healing and less MP than a single Cure II.
Weave DPS between Healing.
Only when Damage does not compete with Healing would it make sense to give Healers more DPS abilities.
As far as Enmity management goes, i remember levelling a lot of DPS Jobs through Stormblood and the prevailing attitude was "Its your fault you took Enmity from the Tank". Even when Lucid AND Diversion were on cooldown.
If they brought back Enmity management for Tanks, they'd need management tools on DPS and then we'd be right back where we started. Or worse, Back in ARR days with geared DPS ripping Enmity from newer Tanks with the only management option being to stop hitting the thing.