MAYBE THE BEST FEATURE In theory, it isn't that much, but Stage Manager may be one of the biggest productivity features yet.
I just installed Ventura today and, to work my way through it, I figured I'd revisit this thread. You're right that Stage Manager is a great feature but, if memory serves, it's actually just giving back a function that Mac had a very long time ago. I recall being able to go the menu bar and click on a button that listed all the apps in use. You could scroll down and select the one you wanted now to use. I also recall being ticked off when it just disappeared with some OS upgrade.
However, I will admit that Stage Manager provides the function in a more elegant manner.