Sage is actually pretty damn solid, the problem they have is some of their buttons are clunky for no reason at all, lemme give a couple of examples.

Eukraisan Dosis: I absolutely hate managing this because we are either always going to clip a tick or it's going to fall off because we have to account for the extra 1s recast animation when we press Eukraisa. Other healers just press their DoT we have to press another button which makes the timing wonky. Just detach Eukraisan Dosis from Eukraisa and make it it's own button.

Phlegma: Again another button that is hampered by jankiness when it doesn't need to be, it locks out your ability to weave it cleanly with Dosis (which is when you would be using Phlegma as it's typically used under raid buffs) just take that hamstringing provision away and let it be a true OGCD.

Pepsis: hampered heavily by the fact it requires shield to trigger which makes it an entire reactionary ability in a proactive kit. I only use Pepsis if I don't have Ixochole or Holos off CD and the party needs an emergency top off for a incoming raid wide. Pepsis for its cooldown probably needs to lose the consumes shield gate and instead does bonus healing when consuming shield.

Fix those things and the SGE will be in an excellent spot.