My thinking is that the P series is just better binned U series silicon since they are extremely similar (memory type, number of E cores, TDP, clock, etc.)
And the most “weak” U series is perhaps also a binned (down) version of the regular U series.
Alternatively the P series is binned H, but it doesn’t sound right consider H series is pretty different. Or they could just be two lines (P and H, for mobile). Chip manufacturing (and tooling) should be highly customizable (a bit like how CNC or 3D printing can make a lot of different stuff), especially if you throw the desktop chips into the mix, this “cross-binning” can just go on forever.
I’m not against this “silicon lottery” thing. Disabling bad cores and selling them with reduced performance is a good way to make use of the good parts, so long as the binned versions are priced appropriately.
Previous U series I think go from as low as 9W to as high as 25W, with factory preset at 15W.
Not until recently I started to look into laptop thermals, but it’s also well known that Intel Macbooks run extremely poorly in part to their awful cooling (their fan have no intakes!)