In for a penny....
I see I've raised more question that answers. Lets see if I can do a better job by clarifying/commenting on members queries. And thank you Griphos for editing your original reply. No I do not work for MS/Xbox. Just another user with a different view to some.
Lets look at the 3 versions in the MP.
Deluxe gets you 5 additional aircraft and airports over the Standard version.
Premium gets you 5 additional aircraft and airports over the Standard version. You don't get the Deluxe stuff.
Premium Deluxe gets you 10 additional aircraft and 10 airports over the Standard version. So both the Deluxe and Premium add-ons.
If I buy the premium deluxe version all 3 version will show as owned as you have just paid for all the aircraft and airports listed in the 3 packages. They are yours to keep.
These bundles are in the MP to cater for users who only bought the Standard or Deluxe versions of MSFS and want to upgrade/get the additional add-ons available in the other versions. Of course Gamepass owners who have installed the Standard version can also purchase any add-on from the store. No add-on purchased at the store is lost as you have paid for them.
If I did not have gamepass and just purchased any of the 3 versions of MSFS for the full price then the version I paid for will be listed in the Microsoft Store under My library. Either as Installed or Ready to install. Select that item and in the dialog box that pops up it will clearly state "You own this game". On the RHS it will either say Launch if you have it already installed or Install if not already installed.
Anyone who purchased the game can verify this.
However, with Gamepass you are given a special digital license. Look under Installed and Open Digital Ownership. It clearly states "This product is installed. You can use Digital Ownership with Xbox Game Pass for PC or buy it to own"
You will also see an entry for MS Flight Simulator with the same comments.
This ownership is only valid while you are a gamepass subscriber the same as any other game you may have installed.
So yes you can call yourself an "Owner" of MSFS Standard edition as long as you keep your subscription active.
Be assured that if you cancel your Gamepass subscription you will lose access to that game and any other game in your library that you are "renting". That is how it works.
If you purchased an MSFS Upgrade or any other product in the MP while still a Gamepass subscriber the purchase will stay there. If your Gamepass expires you will need to buy at least the Standard version of MSFS in order to access those purchases.
The wording of the Bundles in the MP store has been interpreted differently by many users.
If I was looking for a cheap buy-in to the Premium Deluxe version it is easy to convince myself that the wording meant I get "everything" at a big discount over everyone else, why, because I'm a Gamepass subscriber. Even though I might be in my first month and had only paid $1.00. (I'm sure everyone who paid full price would not be happy if this were true).
On the other hand when I read the wording I took it to mean I was getting "everything" as in, all the aircraft and airports in the Standard edition and was being given an option to buy extras should I be interested. This Upgrade appears to be the only option for anyone interested in getting the content from those versions. The are called Upgrades for a reason. Sure the description could have been worded better but it wasn't.
I don't think anyone who purchased an Upgrade can show that "You own this game" without it still showing options to buy it.
To my mind unless I see that ownership clearly in my account then I do not own the product.