An iPad certainly can be used for productivity and creative purposes, but it's restricted compared to a Mac. It makes somewhat better use of its hardware in certain ways (a 16 GB iPad will be less bogged down by swapping than a 16 GB Mac running the same number of tasks). It'll be interesting to see where Vision Pro falls in those ways - my bet is in between, because it's using new, cleaner, iOS-derived code, but its UI probably takes a good deal of RAM and some CPU ,although much of the UI may run on the R1 (is the R1 sharing the M2's 16 GB of RAM, or does it have its own)?
Some Mac code is almost incredibly fusty, although much of the worst didn't survive the transition to Apple Silicon. Adobe seems to have finally gotten all of the Assembly Language out of Mac Photoshop, but that transition is somewhat recent. Anything that still needs Rosetta is probably coded in one form or another of "you don't want to know"... iOS (and iOS derivative) apps generally aren't. There's a guarantee that any iOS app will run on the Mac with a simple recompile. Note that there's NO guarantee the other way around (even if you eliminate Rosetta), even though a well-behaved Mac app should port fairly easily. That is a lot of why an iPad can do more with the same RAM.
Even given the efficiency advantages of an iOS based OS, the Vision Pro is pretty darned processor and RAM constrained compared to a comparably priced Mac... If you want your Vision Pro with 256 GB of storage, the closest Mac is a 16 core M3 Max MacBook Pro with 48 GB of RAM and 1 TB of storage. If you would spec your Vision Pro with 512 GB, you can choose between upgrading the fire-breathing Mac to 64 GB, a 2 TB drive or a 16" display. If your Vision Pro would have 1 TB, choose any two of the three. If it would have 1 TB and a spare battery, the Mac gets all three.
That's a pretty big performance delta to overcome - the 16-core M3 Max is the fastest laptop in the world (by something like a 25%-30% margin over anything except a 14-core M3 Max) on the CPU side, and quite competitive in GPU tests. The Vision Pro is a nice $1000 Ultrabook with a (VERY) clever interface and an efficient, but constrained OS.
As a primary computing device, it'll work if either a top-end iPad or a modest MacBook Air would also serve your needs. If you have that kind of needs, can easily afford $3499+, don't mind a 2 hour battery life and want to play around with a truly cutting-edge interface, great. If you're doing something weird where the VR interface is a huge advantage, it's cheaper than most headsets that are as capable, and it's more capable than any other consumer-grade headset.
The other possibility is that it's a secondary computing device. You are the kind of person who owns a Mac and an iPad, and the Vision Pro is going into the iPad's role (or becoming even another device). If so, you have to be able to afford a $3499 secondary device.
I'm sure all three of these use cases exist:
1.) Relatively modest primary device needs and love/want to try the interface
2.) VR-critical application where the Vision Pro is MORE capable than a high-end Mac because you can see things in a new way
3.) Able to afford a super-pricey secondary or tertiary device.
What I am unconvinced of is that they add up to an Apple-scale market.
