They do support syncing up the workouts of people who're each using their own device: https://support.apple.com/en-us/101979
What? Abandonware? They are constantly posting new workouts that are thought out and well produced. The Fitness+ app is very well maintained. It works great. It has cool features. Honestly I don't know what you are talking about, here.
I've worked out together with one to three other people several times. No one cared that their heart rate wasn't shown on the screen. It's really not an important feature and a very niche use case.