Momo leather is superior in quality to ph3 leather. But the best hide of all is still Connelly.
It comes down to cost. Could be that Alfa needed to use a cheaper leather for the ph3 GTVs therefore the hides selected to tan were a poorer quality , the tanning process different so that it cost less. Also their upholsterers could have used up more of each hide when cutting the seat panels therefore not wasting the inferior 'flanky' leather (belly, around the leg area) to increase yield therefore reduce costs. These areas could have been wasteage and not used in ph2.
Guess my point is that it's less about the brand name behind the leather and more about the required cost Alfa needed to hit for ph2 v ph3.
Also, Momo is a design company that makes car accessories, they're not a tannery. Momo's logo on ph2 seats is just purely a co-branding exercise. Also batches of leather from one delivery to another could vary despite it supposedly being the same grade.... So many variables on what is a natural material. Not like a polyester head lining for eg where you can make 1000s of metres all exactly the same.
Connolly has been tiny since the late 1990s/early 2000s when the tannery went bust. I doubt very much they are supplying Bentley , RR, Ferrari etc in any meaningful way if at all, they don't have the capacity.
What they do still have is an incredibly strong brand name ... People still assume they're pumping out 1000s of metres of leather to all the big car makers and that it's the best!
The best leather in the world now comes out of tanneries in Italy and France and has done for many years. UK = nothing in comparison.