One of the unrealistic parts of alot of mmorpg's is how easy it is to heal a character. I see this in DF too. The amount of damage healed might be fine I guess, but it's the time it takes that is usually to fast.
If, say, only the best portions and heal spells had the time effect that the low quality ones have then maybe we'd see more realistic behaviour in fights as well.
You don't really care much about your hp if it's easy to restore.