It is just enabling a lower tier of customer to operate on the same stack as everyone else.
This is vertical integration, not horizontal integration.
The level of monopolization remains the same.
And even with a monopoly, some of the benefit of simple convenience could come into play when there is acquisitions.
Not having to go to a separate store and maintain separate accounts for different things.
Having a cable company that sucks and a phone company that sucks is not good. If they merged and the service remained the same then now you just have two bundled services that both suck.
Yet, having a bundled plan would potentially be more convenient.
T-Mobile offers streaming services, home internet, and other things that Mint doesn't.