Do people have any faith in the these sorts of notices, when nothing ever produced by the company has yet been supported that long?
Absolutely. If they decided to make this announcement, I have faith that they'll stick with it. Whether Pixel 9, 10, 11 etc. will have similar pledges, we'll have to wait and see.
But that phone would've been paid for by your payments for months 25-48 so that seems fair.
It is suggestive of Google's usual approach to supporting their projects though. I'll believe seven years of updates when I see it.