Yet, you cannot have a link to Netflix or Spotify from their app to their own website as you could subscribe on it.

And the browser is limited to whatever Apple allows. If it doesn't support some web API that has a native equivalent, you're out of luck. There are many of those.

These are all concessions to the user experience that harm both consumers and developers.

You Download the Netflix App and it Doesn't Work if you don't already have an account.