You can filter your watchlist to only display your favorite streaming services already.
Go to your watchlist
Click the “play”-icon.
Select “All favorite” (given you selected them in settings)
Some additions that could be made:
Have the “only favorites” option that exists for “Up Next” on the dashboard availble for Watchlist on the dashboard as well.
Have an option to save the filter as a default for the list.
For Apple you have Apple TV+ (Subscription) & Apple TV (rent/buy) listed as 2 seperate services. Same story for Prime Video (subscription) & Amazon (rent/buy)