Of course I haven't worked with him either, but it is not difficult to prove he has excellent engineering skills. Just watch some videos with him, he is such a terrible speaker that it is 100% sure that his texts are not scripted, but he can explain many things (electric cars, rockets, AI, you-name-it) in very detail, more detail than any other CEO of a multi-billion company is able to. You can also watch videos with other engineers or tech-journalists (who have worked with him or interviewed him) talking about him, like Tim Dodd and numerous others. So, no, it is not only "hearing and saying".