I think you are criticizing an idea for not being a study. I think it's a reasonable and interesting idea, but at most it is something to consider, not some infallible axiom. More akin to "the Peter Principle" than a theorem.
Point 2 is... neither important nor really germane. (I don't care what engineers say, and Musk isn't an engineer anyway.) The point is that people understand their customer bases, and sell to them, and then imagine that means they understand how to succeed in the business their customers are in, and... not so.
It's basically a reminder that understanding the customer is everything. No matter how good the tech is, if you don't solve the customer's problem... they aren't buying.
Yes, when I wrote this article - I was pointing out that we seem to have missed this rather common pattern. And if you understand this pattern you can avoid some strategy mistakes.
I didn't claim that this one pattern explains all of the failures.