Bravo. You have adequately summarized my own feelings on expertise and learning.
I will tell you that I learned even less electronics than you when I was young, much to the chagrin of my ham radio licensed, professional radio technician father. So you have always appeared as an expert to me in that regard.
My personal opinion is that if that uncomfortable, fraudulent feeling ever goes away, if you spend too high a percentage of your professional time feeling like you really have everything figured out, then it may be time to start seeking new challenges to make yourself uncomfortable with.
It's like an RPG. They have to give you a sense of ability progression, some battles have to feel easier, but if the last half of the game is a repeating series of trivial, easily resolved battles, it would be super boring. :)