this is going to seem like a mean comment, but if you are having trouble healing titan HM, or consider it hard as you had said, as WHM at il90, i would not suggest maining it, as titan HM is very easy. if you think its hard, wait till you get to ex primals, which will destroy you as a healer. if its just because you lack practice or you are just getting to that content, or youve finished it a few times on the other class, but are still having trouble as WHM, find someone to help you through it, and try not to pug it. i tanked al HM primals for a friend getting their relic, and she died several times, its not that she is a bad healer, she had never done it before, even thouugh she heals fine in the other lv 50 content we ran.

i only say this because i used to main a il93 WHM, and cleared garuda ex and got to the heart phase of titan ex, which is insanely difficult compared to HM. ive cleared grauda, titan and ifrit ex as a tank, and have seen tank, while only getting successful clears on garuda ex as BLM/MNK/WHM, as my fc only has 1 tank and i decided to drop from healing to fill the gap. i have seen wipes caused by incompetent healers so much, and just as many caused by every role, not trying to pick on healers.

to end it, if you need practice, which might be the case, because you healed through ST, get people from an fc to help you out, and if you truly enjoy WHM, id say main it