I believe that we are yet to observe how interconnections within brain matter more than the actual amount of neurons. You get a lot when combinatorics of these neurons forms huge networks
The only things we have for now beyond receptors are CGMP and CAMP and their modulation by phosphodiesterases. That's not enough, not at all. Although it's true the role of phosphodiesterases is understudied.
And it's NOT about size and sCaLaBiLiTy lile deep blue propaganda make people think, the C.elegans has only 150 neurons in its CNS, 300 in total, and no one has built a simulation. It's true that some receptors are lacking and will only be found in the next decade because of underfunding (because of e.g deep blue) but even then it will not run.
Musk certainly is rational - whether that is always apparent or not is another question, and what level of certainty he requires before taking action is another question - what his risk tolerance is - but all things considered he makes more good and rational decisions than not.
I suspect you're in part basing your judgement off of the shallow level of detail that you see in mainstream media or his Tweets, etc vs. ever seeing/reading much of his long-form writing and thinking to be able to understand his rationale; and perhaps also in part it's that your domain expertise don't overlap enough to be able to understand the other's decisions - to reverse energy his actions or shallow words to understand how it flows back to first principles, which he often mentions working from.