One glaring example is a "real" filing system, I've lost both precious time and files navigating through the quirks of the iOS answer to this. Also I put the laptop into clamshell mode in the office, connecting it to a proper sized display with mouse and keyboard which is far more comfortable to use. I just can't imagine how the mouseless and cramped environment of the iPad pro can match this, especially over long hours of work.Curious that you over emphasise the "real" there. It is what I'd consider real work. I write up multi-page reviews, technical reports, I do artwork for my apps, write up some code to transfer into Xcode later and work on websites. Maybe that's not real work to you, but since my accident it's what I have to do.
I'll give you, not everything can get done on it, there's always a need for a desktop/laptop. But I'm finding that need is constantly diminishing.
But that's even what Apple said back at the launch timeframe of the first Pro. A Mac when you need it and an iPad when you don't. I kind of agree with that.
Again, I guess it depends on the type of work you do, in my case it would be a serious and crippling downgrade.