Modals of Certainty Degree of Certainty

[Volcano1985]

MODALS OF CERTAINTY DEGREE OF CERTAINTY

She is a doctor. is + 100%
He may be an architect. may be 80%
He might be a civil engineer. might be 60%
He could be an art professor. could be 40%
She isn't a lawyer. is not - 100%

Hello, I saw this on british council site

I was taught could is more possiblier than may/might, but I see the opposite here.Was I taught wrong?

[Mister Micawber]

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I think that any attempt to quantify these modals is doomed to failure. The perceptions are idiolectic.
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Native English teacher at Mister Micawber's