I think yes and no for Apple. It's certainly making a ton of money off of each of its devices (Watch, iPad, Mac, etc.), but none of those devices (with the exception of the Mac, probably) would sell as well without the iPhone's ecosystem.
In some hypothetical universe where the Watch and iPad were from distinct companies, they might have to force interoperability with other products like the Pixel or Galaxy Watch to make the iPhone a compelling product.
In some hypothetical universe where the Watch and iPad were from distinct companies, they might have to force interoperability with other products like the Pixel or Galaxy Watch to make the iPhone a compelling product.