Elon musk has don a lot of myth building around himself,for example claiming to invent the hyperloop(which was invented in 1999 by ET3). And his employees are mad about him taking all the credit for all kinds of results.So i'm not sure you should count him.
We also see the same thing with Edison - claiming credit for other people's work.
The most impressive engineer i can think of is altschuler , which in the 1950's, in russia, even after/while being in a russian labor camp - invented a method of systematic invention(TRIZ) that is used to this day, and really enables every engineer to become an inventor.
So why am i mentioning him ? because to a certain extent - coming up with good inventive ideas may not be the hard part(to some extent). But refining the details,building prototypes,testing, etc is the filter that takes a bunch of good inventive ideas and comes with a great invention.
But usually this process takes an infinite amount of work, so it's beyond the capability of a single guy.
