I am quite shocked by the Deatheater cards though, I sort of assumed they would be much more common.
Well gee, it's still quite early, but I expect we might get a higher % of the boxes reported because the people who post breakdowns will be a bigger % of the buyers.
Death Eaters might be about as common (relatively) as they were with GOFU, since the total print run was only half as large for MM.
My impression from the pre-release buzz wasn't that Maggie Smith was going to be the rarest, but that there was a lot of interest because she hadn't signed before. I don't know how I got the impression, but I did have a hint that the yet-another-Emma was going to be scarcer than the Maggie. That wasn't confirmed specifically, though.
Of course, in the early days, people are a lot more likely to bother to post a breakdown if they pulled a Maggie auto than a Sykes auto. Still, the early returns from full cases hint that she was in the "second tier" of scarcity, like the Gambon auto from GOFU. Time will tell. The earliest boxes and cases shipped might be skewed from the total packaging run.
I note that there is about 50% more prop cards (adding up the numbers) than there should be in packs, at 3 props per case. Perhaps we will see a bunch of them in goodie bags at the next SDCC?