There's some decent cyberpunk ideas in part 2, but it's pretty bad yeah. Biggest downgrade though is the art and especially the coloring. I mean you won't comprehend the story either but that's not the deal breaker here. 1.5 is a collection of side stories for a second run of the manga that never meshed as a complete thing. It's as solid, as individual spy stories, as the first volume without the full overarching plot.
I'm not sure I'm sold on your arguments about the Major ethnicity, as the apparent lack of so called Japanese features on female characters is not a reliable element, quite the contrary. She has a Japanese name, works for Japanese intelligence (and in fact counter intelligence mostly working on domestic soil) : I'd actually expect her to have a japanese body model. But it's not really important as body swapping & fluid identities in the cyborg age is pretty much the main impetus for the story.
If you liked GitS, you should probably take a look at the english prints of Appleseed (Vol 1 to 4, even the half finished Vol 5) and Dominion (the first run especially). Appleseed is really, really amazing.
