from my experience, vitamins drop rather fast above 50 and then until 30(maybe less, i rarely loose my EQ buff) they last pretty long....
if you really need to loose food or water to regain vitamins, simply run around, get hurt a bit and use stamina
or try to eat/drink up to 110, which drops pretty fast to 100 afterwards as well. so i guess there are lots of ways to get around such issues
i personally really like the vitamin system as you dont go and stuff 50cooked meat in your face to fill your food
considering how only those who skilled tame riding can farm with them, the tames should have some certain viability rhino should be for stone/metal, elephant for wood/thatch, bear for fiber is kinda fine (fiber doesnt weight much after all) tames shouldnt be the center of attention like in ARK, but shouldnt be useless as well!