In the first place, horses for courses.
Mac Pro's/iMacs are for hardcore computer/video power.
MacBook Pro's for portable power, Macbook 12" for those that like the shape of a laptop and want to go light.
IPads are for lazy folks like me, I carry a 9.7 everywhere, always, anytime.
I use a 12.9 iPad as a notepad (check out Nebo, goodreader), PDF annotating device (Documents5 with paid PDF expert) and book reader. (I'm so bad, I buy brand new study books that aren't available in digital format, have the spine cut off, scan them and the OCR them on my MacBook Pro/MacMini).
I use my 9.7" like an A5 notepad, reading books, reading good quality PDF's, quick reference book, consuming (Three newspapers with good apps, several newspapers on the internet, a little bit of television or series).
Reading on an iPad is natural: portrait mode, full pages, annotating, it's (almost?) quicker to open an iPad then to open a book, having the power of google, knowledge databases like Wolfram Alpha or Legal Intelligence, having every (study) book always with you in 1 pound...
But in some of your problems I might be able to help you a little bit.
iOS seems to be made for doing one task at a time in isolation. Any task that involves grouping data from multiple sources or routing files through multiple apps is hard or impossible.
> that seems like a difficult one, there is the split screen, but I'm not sure how much that helps you.
You can't select a bunch of files at once for moving or deletion.
> you can with Documents5/PDFexpert, I use it as a kind of file browser and it works (for me) pretty well.
There is no AppleScript (SwiftScript?) to automate tasks. I'm not a heavy scripter but I run at least one script every day.
As an example, I sometimes need to process a moderate number (>100) of data files by changing one parameter in each file and processing them again. iOS would have you manually edit each file. In macOS I run a script that does this in under a minute.
>there are some automation apps, there is one called workflow, but I have no idea if this will do your trick.
iOS won't support Parallels to let me run Windows programs. I need to run just one program, a scientific app made by my company.
> I doubt your company will allow you, but I use Jump Desktop for those occasions when I need the power of a desktop and I'm not at home or in the office. Others are allowed to use some Citrix thing to login to their remote/virtual workspace, no idea how it works, but it might be a solution.
iOS doesn't support drag and drop between apps.
>No, not as such, but copy paste does work well (for me, again) and it does work between (Apple) devices these days as well.
iOS doesn't upport as many graphic and video formats as does macOS.
>No, not native, but VLC and other apps might help out. That is the power of iOS as well, the many, many apps that are available.
iOS doesn't support a general print to PDF as does macOS.
>Again, not native, but PDF Print will help out as there are many others that let you print almost anything.
iOS versions of iWork don't export to Word and ppt as do the macOS versions. Numbers doesn't export to csv files.
>I got a "free" copy of Microsoft Office 365 from the university that also works on both my iPads (12.9 and 9.7), Mac mini, MacBook Pro
There is no general place to exchange data, like the macOS desktop, but iCloud Drive is slowly evolving in that direction.
>If you mean by data to select/sort/duplicate files, then again Documents5 is what does this for me.
I really hopes this helps a bit, but as nice, beautiful and useful iPads are, there is no one size fits all. You can push an iPad (Pro) into tasks that it wasn't designed for, but at some point it's wiser to use a better fitting tool.
In the mean time I'm happy I'm not hauling around that old 17" MacBook Pro anymore. Man that was big and heavy and needed some serious protection!
Yesteryear wasn't always better