I was specifically talking about the value of a COOK who handles FOOD. However, the same principle applies. There are ~80 types of alcohol in the game, and they all seem to be weighted equally. So your chances of a dorf having a preference for a type of alcohol you can actually produce/obtain are fairly low to begin with. Furthermore, even if you produce heir favored drink, they aren't gauranteed to pick it up. However, the happy thoughts from drinks are NOT bugged like happy thoughts from foods. Its just that drinks have no quality levels. Thus the happy thoughts from decadent drink are mostly gained from sipping from a high value (full) pot. So a decadent drink can be a Plump Helmet Wine [30] pot, while drinking from a near empty pot would give no such thought... even though the exact same amount of drink is taken from each. The difference is that a masterwork roast that rivals the price of lower tier artifacts will produce the same level of happy thoughts as a raw dirty turnip. In fact, if the dorf prefers turnips he'll gain MORE happiness from the cheap food. Lastly, a dorf isn't even guaranteed to have a food preference at all. There are only 4 preferences that every dorf has: stone, metal, gems, booze. Everything else must first roll to see if they even have a preference (then roll for what exact type).
Don't get me wrong, I still have a legendary cook in all my forts. Its just that they are a luxury position whose quality level only matters for trading. I mostly use them to cook up excess seeds, or cook in ingredients I made for the hell of it (like pressing rock nuts into excess oil, milled flour instead of turning it to booze). I mostly keep one around, though, becuase we really -should- have one. Its barbaric and uncivilized to just shovel random ingredients into your mouth and call it a day. From a strict gameplay perspective, it simply makes no difference, and retraining a new cook isn't a big hassle either.
I'm not saying you have to abandon him, its just that abandoning him isn't really a big deal like it would be for your legendary weaponsmith. Personally I'd keep him as a "seed" to infect crippled dorfs with. Military works best. When a goblin siege comes you can "release the (were)hounds!" Or make him a manager/bookeeper. Or Set up a pressure-plate controlled containment system and keep him as a cook- just pray no one gets trapped inside his room when he transforms.