I’m thinking maybe you meant Newt is the quintessential, archetypal or consummate insider [with which I would agree]. ‘Penultimate’ means ‘second to last in a series’, such as, ‘Harry Potter and the Half-Blood Prince’ is the penultimate book in the series.
So, I stand corrected and am happy you pointed that out to me. Hopefully that will be my penultimate grammatical mistake ...for tonight!
‘Take care,
-Geoff