Answer: For the first part of that, I guess one could almost say that "chords" didn't really exist until Rameau said they did. In his 1722 Treatise on Harmony he established the idea that, for example, E-G-C was really the same basic thing as C-E-G, but in a different inversion. This way of thinking eventually caught on. In previous centuries musicians thought in terms of intervals above a bass line; a sonority labeled 6/3 for an E bass (E-G-C) was a different creature than 5/3 on a C bass (C-E-G). Now we think of them both as different flavors of the same C major chord. The processes of counterpoint produced harmonies, but they were not considered as "chord progressions." There's still a kind of freedom to be found in forgetting about chords and just writing counterpoint. Chords will result, of course.
As for DEFGABC, I wouldn't call it "C Major Dorian," but just Dorian, or D Dorian. Like the other modes, Dorian can be transposed to other starting notes, and it's handy then to call them by their starting note: "E Dorian" would be EF#GABC#DE.
Maybe this is what's throwing you: you've seen a description of Dorian as having a "b3" and a "b7." That's not really a useful description of the mode. Dorian has a minor 3rd and a minor 7th - but those notes aren't necessarily flatted. In the scale you describe, DEFGABC, the "b3" refers to the minor third above the tonic, F. Not F flat.
In the same way, sometimes people speak of a "b7" when they mean a minor 7th, or a "b5" when they mean a diminished fifth. It's just shorthand. But D-C is a minor 7th and has no flats. B rising to F is a diminished 5th but has no flats.
Of course, what really sets off Dorian is its sixth. I probably have said at some time that the 6th in Dorian is "sharped." That's merely a confusing way of saying that it's a half step higher than one might expect it to be. A normal minor scale has a minor sixth above its tonic, but Dorian has a major one; we might think of it as being "sharped" but it doesn't necessarily have a sharp sign; it's just a major sixth, like D to B, instead of the expected minor D to Bb.
