I don’t think the average person is actually capable of guaging their level of satisfaction in life

One could argue they're the only ones who can gauge it.

But there's definitely a struggle to separate the symptoms of happiness from the conditions of happiness.

Like, if happiness is just a chemical, then OD on it and you've successfully maximized the raw score. But if you asked someone in advance if that's how they want to live their lives, I don't think you'd get many eager for it.