Calling someone a bot just because of a wipe is rude indeed and doesn't help one bit but I don't see how they apparently didn't know how SGE worked? And what that was to do with buying a title or not? All 3 Ultimates were released before SGE and nobody is expected to know all classes inside out just because they cleared an Ultimate. Doesn't excuse the bot comment, of course.
That said, Kardia (and fairy autos) is passive baseline healing and nothing more. It's normal for every healer to burn through the whole toolkit on wall to walls while bosses serve as a good cooldown reset because there is so little going on. SGE is no different there.
Reshield the tank on the run while he's still pulling so he starts with full HP when everything is gathered and either dot everything or spam Dyskrasia on the run while the tank is still healthy.
Once he stands still, Kerachole for mitigation and to avoid wasting stacks and Physis + Sorteria because Kardia autos profit from the small heal buff and you can keep dpsing for longer. Can slightly delay both by a GCD or two if you crit shielded and the tank hasn't lost HP yet. At lower levels I recommend sprinkling in EDiag before you completely burned through all the Addersgall stacks to spread healing a bit more evenly.
And as Cheremia said: Tauro when Kera mitigation ran out. 10% for 15s is a lot.
It takes some practice to know how much you need to GCD heal in addition to keeping all oGCDs rolling and when you should start using them and it varies with each group but you'll get the hang out of it. You already took not that Kardia and the occasional shield is not enough, it can only get better from now on.