I happen to work with guys that are not lisenced and are good mechanics/fitters.
An engineer is a lisenced person that holds the authorisation to decide which action is needed to be taken according to the manuals for keeping the ac airworthy.
These individuals i have been working with are good mechanics and stressing again the word mechanics, but they do not understand the function of the components they are changing and most of them tried to pass the exams many times but failed.
So yes to be a good engineer you need to have passed all your exams.
The hand skills will get better as time goes by but you will not get any smarter.
So you underrstand the concept or not,there is no between.
Even if this guy that got gaught was good enough with his hands to work on ac, it does not mean he understood what he was actually doing.