One thing to keep in mind, Philip, is that unlike the wine folks, we really don't have a common language precise enough to describe these things. Most of our terms are so broad as to almost be meaningless. For instance, sugar, molassas, etc. are all described as sweet. But so, too, are carrots. And late-season turnips. And onions. Yet, few would claim that sugar and carrots have the same flavor. And, for sure, neither of them resemble onion. As noted above, there is more to flavor than just the four receptor tastes.
A lot, too, depends on the sensitivity of one's palette. You ask, f'rinstance, for differences between those alliums, when, in fact, there are often greater differences between different varieties of each one. White common onions, and red torpedo onions are both onions, but they have distinctly different flavor profiles. And, when it comes to garlic, give it up. There are on the order of 550 varieties, with vast flavor differences among them. Peple with less descerning palettes might not tell them apart, whereas those with more sensitive receptors notice even slight differences.
Once you throw in other factors, such as heat, you can really come a cropper trying to describe these nuances. Again, with garlic, there are different levels of heat, different parts of the mouth where you sense it, different ways the heat presents.
Even such authorities as Chester Aaron use descriptors that really don't mean all that much. Here, for instance, are a few garlic varieties and how he describes their flavors. I would submit that, after reading them, you really don't know much more than you did:
Siberian: Strong flavor, quite hot.
Armenian: Strong earthy flavor.
Inchelium Red: Mild but lingering flavor; can sharpen with storage
Red toch: Raw taste described as perfect garlic flavor
Chesnok Red: Good aroma and rich, lingering flavor
Xian: Taste is not too hot but very rich
Xian happens to be one of my favorite garlics. Having tasted it I, perhaps, understand what he means by "very rich." But left to my own devices, I wouldn't have used those words. I might describe its flavor as deep and mellow. But, again, unless you've experienced it, "deep and mellow" as as meaningless as "strong earthy."
these foods can all be adapted quite successfully...
Yeah, they can be, Joey. But why would you want to?
Me, I'm on your side: if alliums aren't a food group they should be.