The iPhone entered a market that was already huge and relatively mature, to further expand it in value.
AR/VR is far from that. I hope Apple's entry boosts it a lot further, but comparing it to the iPhone feels like there's only disappointment in waiting, even if it fairly succeeds like the Watch does for instance.
AppleTV was supposed to be a new thing with people developing entertainment apps and games that fit with a TV, not for general computing.
The watch added to the iPhone and had unique apps to take advantage of the sensors.
Neither of these were tied heavily to a macbook or other general purpose device. Unless you mean computing as in anything digital that runs code. Which I wouldn't really call a platform.
VisionOS feels closer to an AppleTV. New hardware with a different paradigm that needs a unique API and new apps built for it.
That said it does seem more like a supplemental device to your macbook + iphone. I doubt many are going to buy it with the intention of it being their main means of computing.
Maybe define what main platform of computing and core product mean if you could?
Not all Apple platforms are enormously successful for third parties.