The sales volumes of the 1TB+ models has got to be fairly low, which makes this fascinating. Since they are being somewhat quiet about it (rather than trumpeting "the 1TB+ models are even faster!") it suggests the P-cores don't yield well enough to support 4 P-cores in the 256GB and 512GB SKUs.
I actually wonder if the 1TB+ models of the iPad Pro represent a higher portion of all models sold than that storage capacity would in other product lines. The iPad Pro is such a niche, weird device; it feels like if you're buying it, you're buying it for something, probably media production related. Its not a Netflix machine.
I figure it's probably just reducing SKUs. The people who care about the fastest chip are likely also the people wanting lots of storage so you can save on having to create a ton more products by bundling them.
You can get Mac Studio 3rd party "SSDs" for less than half the price Apple charges for the same storage, with the same performance, they even use the same flash chips!
Where are you getting this information? Curious because I can't find any evidence that Apple has "much, much, much faster" storage. If anything, Apple storage looks mediocre at best.
While it is not an Apple to Oranges comparison, T710 seems 80% faster for writing big files, and for $279.99 - $299.99 for 2TB this is still much cheaper than whatever Apple is offering.
If you have a better reference (specially if there is something that is cross platform), I would be interested.