There's been plenty of examples on the Internet this past month of people using their iPads meaningfully for work.
In all these cases, the limitations you stated are either non-issues or haven't been enough to negatively impact the overall experience. Or in some cases, what the pros consider to be limitations, they consider to be strengths.
We have a girl who used an iPad Pro to illustrate a book. She likes that apps like procreate are more immersive and less complicated than their desktop equivalents, making the drawing experience a lot less intimidating and distracting.
https://the-ipad-artist.com/dear-tim-cook-abc3fbffba1b
Here's how one guy uses his iPad to record his own screencasts using screen recording and lumafusion. It's definitely something I will be looking at trying out (again) for 2019.
http://teddysvoronos.com/2018/12/04/producing-recording-editing-and-sharing-animated-videos-on-ipad/
Of course, there's Austin Mann using his iPad for editing photos, and he particularly loves the portability, even as he agrees that file management could use some improvement, but the other strengths of his setup offsets the con.
http://austinmann.com/trek/ipad-pro-photographer-iceland
Jonathan Morrison has shared his thoughts about editing on an iPad on YouTube, and even admitted online that he is open to using an iPad for editing on the move in future. We will see how that pans out.
Henny the Bizness shares on how he uses his iPad to create music.
And of course, Macstories using iPads for writing.
https://www.macstories.net/stories/my-must-have-ios-apps-2018-edition/
Just a few that come to mind off-hand.
I am not saying that everyone should start throwing out their iMac Pros and switch to iPads, but it's not entirely accurate to say that the iPad can't be used to work. Yes, lots of areas still can use improvement, while certain tasks remain flat-out impossible, but if you keep waiting for all the blocks to fall into place before starting, no progress can ever be made.
The foundation is there already. I believe that at this point, the people who claim that an iPad can't be used for any sort of work whatsoever say more about themselves than about the limitations of the iPad.