Being in a more competitive industry generally reduces margins but increases the size of the market. Vertically integrated companies lose to aggressively competitive non-integrated competitors
when they exist (and a monopolist is proscribed from buying them all up), because the existence of that competition means they can't be abusive or collect monopoly rents.
Vertically integrated monopolies are sticky because you can't replace any individual part of the stack by itself. You can't compete with iMessage just by creating your own messaging app, because to be on a level playing field you would also have to create your own mobile operating system and design your own phone hardware and microprocessors and convince all the customers to switch despite the existing network effect.
If we made it to a market where anybody could create a new OS and have it run on the existing installed base of hardware, or create a new app in a write once run anywhere language and it could run on every existing device, vertically integrated competitors are at a disadvantage because they have to be best in class in all of their individual markets or else customers find themselves better off to have the ability to mix and match.