I think there should be a real world experiment to test it.
Now when it comes to more complex applications, I'd stop using the CLI if I had to search the manpages or the internet each time for doing something I already did previously. Since I discovered the Ctrl+R shortcut (for searching your history), it has been much easier. You read the manpage once, maybe you do an internet search, you enter the command and then you can find it back as long as it's still in your bash history (be sure to set HISTSIZE and HISTFILESIZE to correct values). I also have a DOCS.txt file where I put all the rare but useful commands I'm afraid of losing. I don't need to be an expert in ffmpeg's options (... though I sort of am now), I can just look at my history or my DOCS.txt file!
(But no kidding: somethings feels CLI very natural, sometimes feels GUI more natural for me.)
"Our product is the second coming of Christ and if you give me money now you'll 100000x your investment!" is the correct answer to all questions when you're in that position. I'm not saying it's admirable, but it's what you do to keep money coming in for the time being. It's not that deep.