Trying to understand benefit of upgrading?

For you, there probably isn't much benefit to upgrading currently as you won't really see increased connection speeds over and above what you're getting now.  You are getting your full Internet speed or close to it, so unless you upgraded to a faster incoming speed you wouldn't benefit.  Also, if you don't have any devices that are WiFi 6 capable, you won't take advantage of the AX capabilities anyway.

That being said, WiFi 6 supports more devices, but you seem to be covered adequately now, and provides better coverage with fewer satellites typically being necessary.  Previously, I had three satellites on my Orbi AC system, but get the same coverage now with just one.  It also will provide somewhat higher connection speeds, especially for WiFi 6 devices.

Finally, you can use your existing satellites with the Orbi AX system, but they must be hardwired to the router in order to work.  And, of course, anything that connects through those satellites will only get an AC connection.

Good luck in your decision.  Sometimes it's hard not to upgrade to the latest and greatest, but it doesn't sound like you'd get much benefit from an upgrade right now and prices may come down if you wait a while.