I wholeheartedly agree. While these potions may be of use to melee for a little bit of added damage, the MND and VIT potions are comparatively useless as consistency is needed when it comes to damage reduction and healing. Having an extra burst of defense or healing doesn't help much, because either one of two scenarios are present:

1: You're doing just fine when the potion isn't in effect... so no need for it.
2: You NEED that potion. In which case when it wears off, you're fucked.

Well, ok, there is a third option where the tank is SLOWLY being whittled down faster than you can heal, and it's JUST enough of a problem that 40 seconds of bonus defense or healing can keep him up. However, being just in that exact range of difficulty is so wildly unlikely that it's pretty much a moot point.