would this be OP?

[Grimoire-M]

Regen is used to mitigate the auto-attacks. It’s the responsibility of the regen healer to cast it on the MT to mitigate them.

If you’re casting a Regen to mitigate a large amount of damage, you are healing incorrectly. You don’t use Regen after a tank takes a 60,000 buster; you use either an oGCD to top them up or you cast a GCD heal (Cure II/Benefic II).

On the other hand, it's both healer's responsibility to keep everyone, including the main tank, alive. You do feel the difference of not having two regens on a tank in Savage and Ultimate. There are high mobility/AoE phases that you don't have the time to babysit the tank's HP while keeping everyone else alive that they don't want to move into your AoE range for. Precasting two regens on them solves these issues. SCH's Fairies both contribute to this passively at no MP or GCD cost but doesn't get the benefit of getting to regen multiple targets. WHM and Diurnal AST both have ways to do this via their GCD and can multi-regen both tanks in two-boss fights. Whispering Dawn also exists as an AoE regen on a far lower cooldown than Collective Unconscious and Asylum at a strong enough potency to match a WHM and Diurnal AST using Medica II and Diurnal Helios respectively.

If you want to make up for the auto damage, you basically have to sacrifice more GCDs than a WHM would to make up for the disparity in Noct Sect. GCDs you sometimes don't have.

Playing Noct AST in duty finder when the WHM doesn't regen is absolutely awful for this reason. It's worse in Savage because you and the tanks have to make up for it.