Even if we assume that a good chunk of that may be "duplicate" in terms of functionality (e.g. todo apps), that is still just a completely different dimension of apps and use cases covered by android natively.
That said, Google Play is not really the thing to compare this too. F-Droid could be. Summing up the "Show all ..." counts, F-Droid clocks in at 6147 apps, and it started way earlier (2009? 2010?).
Some of these F-Droid apps (specifically those created in QtQuick or Flutter) should also run with very minor tweaks on #MobileLinux.
Also, there's more than these 720, some are just very hard to evaluate (because they are for hardware or services I don't have/use), which then keeps me from adding these apps.
It's Linux, if you need something you or someone else will eventually write it. But first there needs to be acceptable, working hardware. Enter the FLX1/s, and we come full circle.
Besides, open-source doesn't have to be GNU, there are a bunch of open source apps on F-Droid.
I don't need more than a handful of apps, one being a browser. These already exist.
I'm glad Waydroid is a thing for folks that are, and sorry attestation prevents full compatibility. But neither issue should get in the way of investment in modern Linux phones, which I've been desperately waiting for, for years.
Web apps are still a thing as well, believe it or not.