Right now the effect of food is so small, and it lasts so short that you typically never use it. I suggest making the effect of food either permanent, or 8 hours, but make it so that you can only have 1 food buff on at a time, i.e., consuming another piece of food changes the buff. This would allow food to be a viable way of further character customization.
To be honest, this is how I would differentiate magic from alchemy, but - since D:OS has food and no starvation mechanics - it could work for food instead of potions.
Like you have suggested, food should give characters long-term-mutually-exclusive-buffs (one buff at the time which lasts minimum for an encounter). But I also suggest the following...
1- Any comestible piece of food should come with a buff as well as a debuff, in order to make eating an interesting tactical choice.
2- The most complicated recipes (the one made through crafting) should have far better buffs then debuffs.
