Perhaps you haven't sim checked as many pilots as I have in recent years. The decline in manual flying skills is horrifying.
Yes, I can fly, well, smoothly, and accurately, because I was well trained many, many years ago and then always kept my skills sharp, flying raw data often in a variety of aircraft. A reason I quit was that I was told by a training manager that I shouldn’t be doing that. I wasn’t going to keep taking the salary if I couldn’t do the job and I know that you have to fly by hand often and not in only the easiest circumstances to retain that capability. He didn’t, or he did but he was too frightened to trust the crews he was signing off to let them (he was an airbus man of course).
So no, it’s not an assumption, it’s an assertion based on experience. It’s backed up too by many recent crashes and serious incidents involving pilots who simply couldn’t fly.