The genetic variance in magical ability (at least, independent from general intelligence, studiousness, etc.) is limited to at most three discrete levels. So strictly yes, it's possible that 'some Muggles are less magical than others', but there certainly isn't a spectrum of magicalness.
Agreed. (I've also made a small clarifying edit to my previous comment.)
Everything that you've said is correct; I was just confused about what ‘blood hypothesis’ meant until I reread Chapter 22.
ETA: There is now a third thread, so send new comments there.
Since the first thread has exceeded 500 comments, it seems time for a new one, with Eliezer's just-posted Chapter 33 & 34 to kick things off.
From previous post: