What is the major benefits of managing streaming services with Apple TV instead of directly with the provider?

AppleTV plus is Apple’s streaming service. It has nothing to do with paying for or watching other streaming services.

AppleTV is an application provided by Apple. It aggregates multiple streaming services into one place to watch, search content. Regardless of whether you used Apple Pay or subscribed to the service as a channel.

Simpler to manage - one view for all subscriptions and same invoice sender.

Some streaming services will limit viewing to AppleTV app only , if subscribed to as a channel.

Some don’t.

I subscribe to various streaming services, none as channels in the AppleTV app. The only time I did was when Apple offered Paramount Plus and Showtime as a subscription for a reduced price, before they merged and became one service.

I personally don’t see any benefit to doing so now.

The only thing I absolutely do is use Apple Pay for all of them, as I can see and administer my subscription services under a single screen on my Apple devices.