FFXI had the same problem. Lots of potions, but absolutely no reason to own them. Their lengthy cooldown and weak curative ability makes them essentially inventory+1 items at all but the lowest of low levels. And to be honest, I could never understand it. I've played countless MMO's which have far superior curing items, and their impact on gameplay is negligible. People don't use them instead of a healer (which is the backwards logic most use to argue against stronger potions), because healers still do the job better... and for free!

Still, I don't think they'll ever make potions useful in a Final Fantasy MMO. The only useful healing items in FFXI were the megalixirs (full HP/MP) which could only be obtained in PvP and special raids, or Primordial Brew which turned you into a god for 3 minutes. I randomly got one of the latter in Walk of the Echoes... I was champing up the subsequent fight with insane damage, crazy regen and 9999 hitpoints.

...ahh nostalgia.