I think those who say iPad Pro cannot be used as a main device are just scared to give up the old way of doing things. The mouse is comforting for them. But touching the OS directly is no less a 'real computer' and opens way more possibility.
Really the issue is only in getting the app developers to make more desktop like apps for the pro.
To be fair, I think the main reason isn't fear but indifference. It takes time and energy to experiment with a new system and way of doing things, and in a sense, it's a gamble because you can't be sure whether the new way of doing things is any better than the current one.
If it works, congrats. If not, you have just wasted all that time and energy and resources for nothing. In this context, if the person is satisfied with their current way of working, they may not see the point of trying to change it because they don't think the benefits offset the amount of effort it takes to try something new.
For me, I made the jump to the iPad because the work laptop issued to me for my teaching just wasn't getting the job done (for me). Don't get me wrong, it was a decent piece of hardware, and all my other colleagues were content to connect it to their projectors and annotate on word documents and screen YouTube videos, and in all fairness, they still do a very good job of teaching.
But for myself, the inconveniences were simply piling up one after another. Inability to annotate on PDF documents (which is solved with a $10 iOS app). My colleagues worked around this by taking screenshots and pasting them in PowerPoint. I started using my iPad more, connecting it with a VGA adaptor at first.
Then came uploading all my teaching materials to Dropbox so I can access and review them on my iPad at anytime, at any place.
My classroom had no visualiser (a deliberate decision by my principal to promote usage of the smartboards). I bought a cheap iPad stand holder and used the camera to project documents onto the screen.
Then came the inconvenience of having to go to the front of the classroom to control the iPad when you find yourself at the back. The Apple TV solved it (somewhat). It would take iOS 8 in 2014 to make this a fully complete and viable solution. This would prove to be especially useful this year because one of my classrooms had the projector cable placed in an extremely awkward and inaccessible corner of the room. I just connected my Apple TV to the projector in the centre of the room, and continued teaching in whatever spot I wanted to be.
Now, with my 9.7” iPad Pro and Apple Pencil, I am happily writing on PDF documents with ease. In for a penny, in for a pound. I am never going back.
It wasn't all rainbows and roses though. The biggest challenge is having to build your infrastructure from scratch. My school wifi blocked the AirPlay protocol, so until iOS 8 brought with it peer to peer AirPlay, I bought my own router. Which meant also getting my own 4G dongle and signing up for my own mobile data plan, if my iPad was to stay connected to the internet. My Apple TV, the 10m long HDMI cable, misc peripherals and accessories. All paid for out of my own pocket. And this connection wasn't the most stable in the beginning, so it sometimes meant putting up with lag and loss in connections (which meant more troubleshooting). For classrooms lacking a projector with a HDMI port, it meant simulating AirPlay mirroring using Airserver (running off my MacBook Air).
Then it meant finding the right apps to get the job done (which again meant spending more money, sometimes buying multiple apps and testing them all to see which is the right one for the job). Sometimes it means having to make do with a subpar solution until a developer "finally" releases that app that is perfect for your needs. And sometimes, it means having to go the extra mile to make sure you are not an inconvenience to your colleagues (for example, I can't access my school's network drive from my iPad, so I have to sure I have necessary documents and files preloaded on my iPad prior to any meeting or lesson).
It helped that at the time, I have a iPad champion in the form of Federico Viticci from Macstories to show me that working from an iPad was possible. Many of the apps I use, I discovered only because he recommended them on his website.
TL;DR - I am not saying the switch to an iPad is necessarily an easy or straightforward one, nor is success automatically assured. What I am saying is that it can be worth it, but you must want it, and be willing to go the distance.
*Typed on my 9.7” iPad Pro using the onscreen keyboard via the Tapatalk app.