"...but it will be a redesign..."
As I said, char limit, but that was a thought of mine as well. But not necessary.
But, you say that something "would/will outshine" - that's an assumption of your part, not a logical necessity. It's possible that a new healer with those traits would NOT outshine. AST was initially undertuned, if I recall correctly. A melee/TP healer could be balanced by simply making its DPS roughly on par with a SCH's "nominal" (not great but not poor player) DPS. It would be "easier" since it would be passively part of their "rotation", but that doesn't mean "better". Again, a RDM that heals instead of casting DPS abilities, but has something like PLD's Riot Blade as a 3 point melee combo would fit in just fine with the current meta and give people a "different" feeling healer to play. Dancer/Blue Mage could fit.
I do agree that buff/support and debuffing really isn't fleshed out in this game enough to warrant a separate entry, though. But there are possibilities.