It’s interesting the Classic app supports the new API apps also, works just fine here.
So there’s no real reason to retire it, you can keep both apps. The Classic app has more features and highly customizable while the new app has a more standard interface but both groovy and new apps run on both ST apps.
The Classic app cannot current “install” the new API apps, once installed it shows up in the Classic app and can be used. Vice versa the new app cannot install groovy apps but once installed it shows up and works fine in the new app. However I believe that the new app has the ability to install groovy apps but it hasn’t been enabled yet.
Overall the groovy apps appear to be more functional and flexible then the new API.