I got ruined for regular coffee when I found a local shop that roasts its beans sorted by size . So it doesn't taste scorched. Apparently most commercial coffee makers roast them in arbitrary batches, which means by the time the big ones are roasted the small ones are burned. I know there's a lot more that can be done with roasting. But that one small change means you can have strong coffee without having burned coff…
Generally the beans are roughly the same size, and what you called burned, I believe is simply because it's roasted darker to compensate for the less than ideal quality of the beans. The fact that WBC finalists are using coffee that the roaster haven't sorted based in size tells a lot. Perhaps the farmer does it to some degree.
I'm not sure if you've looked at espresso chemical papers (mostly the Illy ones), but they're pretty cool and they might explain this.
The oil extraction curves are non-linear. Lighter roasts that aren't at risk of burning smaller beans can be paired with variable bean size to produce a spectrum of related flavour notes, providing a bit of depth to a varietal that has a very strong and pronounced (but limited) set of notes.