My initial thought is that makes no sense from a man who prides himself on supply chain optimization. Going from three screen sizes to four? And then on top of it your only making them 1" apart? Yeah, that's going to cause A LOT of consumer confusion. Trying to explain the screen size is different, but one is a "pro" and the other is "consumer"? Try it on your parents or your non tech friends and see how that goes.
The confusion would come from the 1" difference in size.
Having different screen sizes is not an issue; Apple did it successfully for decades with their 13", 15", 17" configuration.
The screen size difference between those is obvious, and they cater to different users/use cases.
In my opinion, Apple should expand (or rather, bring back) their lineup size-wise to an 11", 13", 15" 17" configuration, while keeping the Air/Pro separation. Air would be thinner, lighter, less ports (as it is now), cheaper, and the Pro would be thicker (to this accommodate more ports), heavier (necessary evil), but more powerful (discrete graphics across the board, for example).