I have found this to be absolutely true. I prefer my iPad to be highly mobile. And with a keyboard case or such that mobility takes a bit of a hit.
That said, I don’t use the iPad as much for “highly mobile” stuff anymore. So, what I’m hoping is that my iPhone X will be sufficient for the mobile stuff I do: triage, reading, other media stuff.
If so, I’m going to invest in at least a 10.5” iPad Pro. I will probably go all in and shoot for a 12.9”. I will likely keep it in a keyboard case and use it when I don’t want to pack my “massive” MBP (13”) around.
I can do most of my productivity work, including web app development with the iPad, but there are definite compromises.
That said, my current array of devices is 2 windows laptops, a MacBook Pro 13”, an iPad Air 2, and Galaxy S7 Edge (which is being replaced with an iPhone X as soon as T-Mobile can get it to me.
I desperately want to minimize my gadget requirements.