I don't think this would hold up in court, and I hope it wouldn't persuade a jury. One of the things that jumps out at me is that those two different perceptions, "circus barker" versus "deadly fucking serious", are highly subjective. Gender-biased, even. On of the things that women in STEM often complain about is our willingness to smile at a man being stern while shaking our heads at a woman acting that way. That's not to say I disagree with you in this instance; I actually see it the exact same way. Musk is a head-in-the-clouds showman type while Holmes was sober and stoic. I just wouldn't trust myself to make an actual ruling based on those perceptions, and I'd hope our legal system doesn't either.
The real difference between the two that I see is that Musk's borderline-fraudulent statements are intermingled with true statements about the actual companies he operates and the actual things they do. That's what buys you some slack to make outlandish statements: Accomplishing outlandish things. If Holmes had normalized electric cars or launched some reusable rockets, and had then staked (some of) the reputation of one of those companies on claims about a non-existent blood test, there may not have been a trial.
Well, normal human discourse isn't bound by the very specific rules of a courtroom.
I figured someone would suggest there's a gender issue at play in my distinction, and I think that's inevitable and unfortunate because I'd be making the same point if they were both men or both women.
Another factor I somehow managed to omit is that Musk's predictions are far enough off to be seen as aspirational, not statements of actual forecast. He said we'd have Tesla Johnnycabs by X date, but then no real movement on them happened, and self-driving proved harder than expected, and so far nothing has come of it. That's barker behavior. That's making noise to get headlines. I think it's still stupid and unserious and fundamentally not honest, but it's not fraud.
Holmes outright lied about what Theranos could do, and behaved (we now know) in ways that showed she KNEW she was lying and that the repercussions would be significant if Theranos was exposed, all while enriching herself from it. That's fraud.
The real difference between the two that I see is that Musk's borderline-fraudulent statements are intermingled with true statements about the actual companies he operates and the actual things they do. That's what buys you some slack to make outlandish statements: Accomplishing outlandish things. If Holmes had normalized electric cars or launched some reusable rockets, and had then staked (some of) the reputation of one of those companies on claims about a non-existent blood test, there may not have been a trial.