Definitely pros and cons. I remember reading that because of the tight integration with iOS this allowed them to achieve best in class latency for iPad + pencil that couldn't be achieved on any other platform. Having followed Oculus / Quest development that low latency is not optional in this context and every millisecond counts so I can see why they would go this route.
On the other hand, the closed ecosystem is definitely cause for concern. Fingers crossed that WebXR support comes out from behind a feature flag to allow for progressive (spatial) web apps.