While you're right that Healing threat needs to be managed it's not impossible by any means, challenging sometimes sure but not impossible.
Titan in particular it's mostly phase 1 where you'll have issues.
1 WHM/1SCH:
This is the optimal layout as far as I'm concerned. During phase 1 keep the tank healed, with his first set of jumps just let the SCH top everyone up - you should have used Stoneskin on the entire party anyway so the damage will be mitigated for the most part. When the second set of jumps starts you can pop a Medica 2 with no problems, he'll likely change phases then so stack up in the SCH bubble and if need be pop a Medica 1. The Medical 1 is probably optional if your SCH is on point but don't be afraid to use it if necessary.
Depending on how things go you'll probably be hovering around Yellow agro then, if it ever flicks into Orange during Phase 2 (or you just feel the need) then pop Shroud and you should be fine for the rest of the fight. There's no real harm in popping Shroud near the start of the second phase anyway just to be safe. Healing/mp consumption is pretty light until Phase 3 commences.
From that point on you just pray people know how to keep out of AoEs and keep the tank topped up during Titan's large upheaval chain in Phase 3. Agro will not be an issue from Phase 2 onwards.
2+ WHMs (harder):
If the party forms into a crescent formation (think semi-circle) around the boss in Phase 1 you can split your Medica/Medica 2's between the party somewhat evenly, preferably with all the ranged on one side to help with positioning the heals easily. The more targets you hit with Medica the greater your threat. If you manage to build into high agro anyway you can Shroud after the first phase change. The rest of the stuff above still applies.
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I'm seeing a lot of groups running with three Healers (2WHMs/1SCH) which isn't really necessary by any means but would make keeping the tank topped up during Phase 3's upheavals a lot easier. If your group is doing that then you best hope all the DPS are on-point during the Heart phase or you'll be enjoying a wipe.
Really the main challenge in Titan is positioning. Only takes a single misstep to wipe.