> But research has shown that people translate vague phrases like "a decent chance" into probabilities in inconsistent ways.

That is not a bad thing. It captures uncertainty, unlike the fake number.

> For an ML researcher who is already used to dealing in next-token probabilities that aren't rigorously determined, just stating a probability estimate directly is very natural.

Exactly, it is a rhetorical device to persuade a technically-inclined audience. It works because it implies that a quantitative model exists. I want a clear, incisive set of mathematical arguments. Otherwise, I’m ignoring predictions as the ramblings of arrogant idiot rich kids.

Saying 50% likely very clearly implies there is no quantitative model to anyone who deals with probability, predictions, gambling, financial markets, ML/AI and so on. The lack of precision is something to pay attention to.

You may decide that the person doesn't know what they are talking about, but that's a very different issue.