I genuinely think that when Apple looks at the Surface it confirms that they made exactly the right decision by not trying to combine iOS with macOS. Billed as the first ever “no compromise” device, it is in fact very heavily compromised, more so than the laptops and tablets it claims to surpass. The Surface isn’t as good a laptop as a MacBook, and it’s nowhere near as good a tablet as the iPad.
I do see some people using the Surface, but never have I seen someone use one that didn’t have the keyboard attached. The Surface is seen by consumers as a thin windows laptop where you can conveniently scroll webpages or documents by swiping on the screen. It isn’t used the way an iPad is used.
Just because you can do a thing, it doesn’t mean you should do that thing: has Jurassic Park taught us nothing?!
The iPad & iPhone get to be light on their feet and forward looking because the Mac is there to do the heavy lifting, and Apple is never going to do anything to drag them down.