I don't use my phone for much of anything but calling and bored web browsing anymore, but I'd genuinely love for my iPad to be more functionally useful, but the issue above is similar to a lot of other interaction limitations. I really can't imagine using any mobile app on my desktop, and I can't imagine using any of my desktop apps on mobile (admittedly the desktop apps I use are on the more complex side things.)
The biggest obstacle to a genuinely productive UI on mobile, I find, is the lack of pervasive and easy confirmation and error-recovery for potentially-unwanted inputs. System management interfaces (e.g. community-built "recovery/modding" environments) get this right (everything that's potentially unwanted gets a "perform a swipe to confirm input" prompt), but almost nothing else does.
Not OP... a BT kb/mouse has been a great consumer-friendly boost on larger tablets for me but sadly... lots of applications (on Android) don't really take advantage of this. They are still very heavily optimized for touch-only.
Example: MX Player (my fav Android player) does a great job binding keyboard presses to actions (spaceBar: pause; arrowKeys: forward, back, etc..)
In contrast, VLC for mobile lacks this "polish". Mobile browsers are another example where actions could be optimized for mouse input but I haven't come across a browser yet that acknowledges mice as a separate input source.
fyi (for anyone interested in tablet to laptop conversion to lessen gorilla arm):
Zagg Folio for 10" tablets (basically turns a tablet into a laptop). I picked this up a couple of years ago (not too many available for Android, most are essentially flimsy stands). They also have similar for smaller handhelds:
https://www.amazon.com/Bluetooth-Keyboard-Android-Tablets-10...
Using a keyboard has been absolutely wonderful though. It's even saved me a few times when I didn't have my laptop with me and had to ssh into work servers for issues.