The way we detect "design" as functional arrangement of components is by observing a functional arrangement of components. We need not understand a priori how that arrangement has been brought about.
I think you could clarify this point a little more because it works for me as well. The way we detect "design"(insert definition of design) is by observing (insert definition of design). Your argument is the same argument that is used by ID proponents.
As for your second point, I do admit my
a prior assumption, the reason I admit it is because if a designer is the conclusion of the argument, it must also be the premise.
Also, the "how" question is precisely what science tries to discover.
Randomly distributed variation followed by selection can also create such systems.
Although I disagree, I understand your point in relation to evolutionary biology. Philosophically, however, I have a hard time attributing design to randomness. If randomness is responsible for complex life that is capable of creating designs, randomness is the ultimate designer.
Intelligent Design is "unscientific" only because at this point it is nothing but an unfalsifiable assertion which contributes nothing to our understanding of nature. Unfalsifiable propositions are by definition unscientific.
I disagree that ID contributes nothing to our understanding of nature because it is literally an idea that seeks to understand the functionality of nature as if it was intentional.
I don't know if ID falls into the category of "unfalsifiable". We can at least understand intelligent design when it is the result of human effort. because we understand what it takes to design a system, it is hard not appreciate nature when viewed through that lens.