So Xbox Series is trending only slightly better than Xbox One did at launch.
I can't remember, did Xbone have supply constraints at first too?
It's not trending only slightly better, it's doing significantly better if VGC's estimates are correct. While it took XSX|S some time to get ahead due to supply constraints, the actual baseline at the comparable point is 60-80% better.
A caveat is that the Xbox One didn't officially launch in many countries until September 2014, so this isn't a proper 1:1 comparison here. Nonetheless, the XSX|S is on track to build a sizeable lead up to the point of the Xbox One's early price cut in June 2014 and the launch boost of September 2014. Momentum is good enough for the XSX|S to stay ahead even beyond these notable Xbox One bumps, and like you may remember from Switch vs. 3DS comparisons, the sales curves will show up as markably different once the console of the previous gen runs out of its bumps to the baseline.
So while the current 60-80% advantage in the weekly baseline is overblown, an actual advantage in the area of ~30% should certainly be sustainable.