I don't know why the upload feature has been removed from the modern version of Connect, or why a manual upload feature can't be included with Express for that matter???
What will I do when activities on my device don't automatically upload to Connect? This has happened a good few times already and the only way I can get them off my device and onto Connect is by manually uploading them using the 'upload' option. If the option to manually upload files is taken away from Connect it will make things very difficult as if it doesn't upload a workout automatically it blocks all future workouts subsequent to that from being uploaded.
Also there are occasions where I will use a different device and upload the .gpx file to Connect to keep all my workouts in one place. Removing the manual upload takes this option away from me.
All in all I think removing the manual upload feature from the modern version of Connect is a big mistake and one that should be rectified immediately.