Learn English – Instruction while drinking milk – Don’t spill the milk; what about solid food

At least in regular, casual use, you're not going to find a real single-word equivalent for what you're looking for. However I'd like to address some of what you wrote:

First, "smells" on its own will only have one meaning, and that is a bad one. I cannot imagine a situation in which saying "it smells" would mean that something has a pleasant odor.

As mentioned in comments, "smells good" is actually the preferred or most common way to say it. It doesn't have to be the exact phrase "smell good," you can attach any adjective to it that you want. It just needs to be the adverb for "smell." You can twist it around and use it as an adjective, too. For example, you can have cake that smells delicious or you can have delicious-smelling cake. This phrase is more versatile than it seems, and you can use it with other words too, like taste. This is not to suggest that using other words are wrong, just that this is the "normal" way to say it.

Third, as for "rarely used loanwords," I'm not sure that the three you suggested there are really candidates for this description. Aromatic is commonly used, however if you were to say it I would think you were trying to sell me bath soap or something. Nevertheless it is used, and it can be used as the word that you are looking for, one that refers specifically to something that smells good, but ultimately "smells good" wins because it's used more. Delicious... rarely used? Are you talking about a "delicious odor" or something? Because delicious is a very common word as long as we're talking about food. Fragrant is also used fairly often, but it refers mostly to "things" and not to food. It's more about the property that something has intrinsically of smelling good. I also disagree that they refer to intensity of an odor. Aromatic and fragrant specifically refer to something that smells good.

So is there a better word? Honestly you can take your pick from just about any of the things you listed, but "smell good" is a perfectly fine two-word solution where you don't really need one word. You can twist it grammatically to be used like a single word, so you're not really limited, and you can change "smell good" to "smell delicious" or "smell wonderful" or anything you want.

Ultimately I think the more interesting question here is why from "taste" we get "tasty," which means "tastes good," but from "smell" we get "smelly," which means "smells bad."

This practice is more common than most think. While there are many reasons for not eating dairy, yet consuming meat, the most common I have come across would be that once people learn that milk (dairy) comes from cows who have given birth (a lot of people do not put 2 and 2 together), they reject dairy on a clean conscience principle, as that milk should be for the calf not human consumption. There are also the individuals who are lactose intolerant. The same mentality stands for eggs, as eggs are technically chicks or chicken periods. However, most eggs sold for human consumption are unfertilized. But I digress. Essentially, the only term I have come across for this lifestyle diet is meatatarian. I follow this lifestyle diet, but always just explain I do not eat dairy, but I do eat eggs and meat (and obviously vegetables, fruits, beans... etc.).