If you really want to obsess over this, I'd recommend reading George Lakoff's "Women, Fire, and Dangerous Things: What Categories Reveal About the Mind".
It touches upon topics like how not all cultures handle colors the same way. Some only deal in light/dark, and don't really deal with what European cultures think of as "color".
Personally, I don't see these as sub-categories of sweetness. I see them as a different facet of taste. Non-sweet foods can be what I think of as 'dark' and 'clear' just as easily as sweet foods can be. I think that it's more typical to call those categories 'rich' and 'bright', though ... but I'm not sure if they're exactly the same categories that you've come up with, or just that they're correlated to those categories.
It's possible that your 'dark' category is things with bitter notes in them (chocolate and coffee definitely qualify) or other flavors associated with more complex chemicals from cooked sugars (like in caramels, which can be developed when reducing syrups), and the 'bright' category is those with more simple sugars and possibly a sour note (citrus and other fruits to a lesser extent).
Of course, my definitions for the categories makes grapefruit more difficult to classify, as it can be both bitter and sour, but we also get into issues of classical vs. prototypical categories, where classical categories require some objective criteria for inclusion, while prototypical categories are more about how subjectively similar things are to other items in the cluster.
And it's important to note that categories don't exactly "exist" -- they're a construct that help us to make sense of things, and so of course they help individuals reduce mental processing necessary to deal with many different things. So we have categories like "root vegetables" and "tubers" which have differences, but is everyone sure what you mean when you talk about them? An onion clearly isn't a tuber ... but is it a root vegetable?
(See https://cooking.stackexchange.com/a/3027/67 ; as people have commented about how it doesn't align with the categories uses in other countries for fruit based condiments. Also note that there are categories that aren't shared across all English dialects -- summer squash, neeps, floury potatoes, pulses, etc.)
Categories also help change how we look at things (also called "framing") -- once something has a name, we can talk about it. So how we used to talk about mushrooms being "meaty", but now we talk about "umami" which includes other foods high in glutamates like soy sauce and hard cheeses which might have been called "savory" but not "meaty".