You get worse w more practice? Explain. I have been practicing the riffle shuffle w/o using the table and keeping the cards contained -- am I going to get worse at it?
From a probabilistic standpoint, even if it isn’t a perfect Faro shuffle, almost-Faro shuffling clearly introduces far fewer bits of entropy which is less than ideal.
Perhaps we can caveat that the person is not cutting perfectly at 26 every time and performing perfect out faros, then we can assume they'll be mixed enough. :-)
It's been a while since I've read Persi Diaconis' paper (who coined the 7 shuffles thing), but I believe all your main concerns were addressed. Not sure about the sleeved deck thing, that wasn't probably a consideration.