if you take any EX trial or coil fight it will be difficult to insert a support job inside. Esp. before the echo nerfs. Competitive content really needs the trinity to cut it. Same with 4 man dungeons will you replace the tank, the healer or go with a solo dps?

And in PVP well... lol

Could work with 24 man "raids" but outside of this i dont see any use for a support job. I mean a real support with pretty much no dps, not like the bard.