SGE is a 'barrier healer'. Like SCH, they're designed to effectively slow down the damage rate your allies take rather than restoring missing health quickly like 'regen healers' that are WHM & AST. They do have tools to do the otherwise, but if you approach them the same way as you play your WHM, you are more likely to run into trouble.
Kardion is a maintenance tool that's slapped together with your damage kits: it rewards you better by playing proactively/aggressively. It saves you more healing needed to be thrown the more you dps. If you're bored you can even switch Kardia partner around to heal those chip damages your other party's taking (I did this sometimes and it's quite fun). That being said you should not rely 100% of time on Kardion for healing. Additional needed healings are covered through a good use of their abilities such as Addersgall, Soteria, Holos, Physis, & (Pan)Haima; additionally a special mention their current capstone ability, Pneuma. Healing spells are their last resort. Normally you wouldn't even need to touch these outside prepull E.Diagnosis/E.Prognosis.
If the player can semi-plan it ahead, SGE is such a beast.
