Will he then be one of the all time greats winning 5 championships and in two different teams? Just doesn't sound right.
I suspect this won't be a popular opinion on a British forum, I think he is, or is certainly close, to being one of the greats. You've just got to look at his debut for Sauber and what he achieved at Toro Rosso to see he was going to be one of the top drivers, and drives like his in Spain in 2010, where he finished on the podium despite having no brakes, is probably up there with Schumacher's drive there in 1994.
Sure he had the best car for two of his titles, but he beat a decent (and previously highly-rated) driver both times and in a similarly performing car he beat some of the undoubted all-time greats in Alonso and Hamilton in the other two seasons he won.
His ability to consistently go from zero to opening a several second gap within a lap in his Red Bull days was unparalleled and unprecedented.
He's not been quite the same driver since he became a father (flying home between tests the season Ricciardo beat him showed his priorities had shifted), but I don't think that tarnishes the reputation of what is one of the most dominant drivers of recent times, alongside Schumacher and Hamilton.
He has different qualities to Hamilton (he's no longer quite as consistent as an in-form Hamilton and Alonso and has seemed under an awful lot of pressure since he joined Ferrari, hence the frustration on the radio and more mistakes) but it's easy to forgot he's done things Hamilton couldn't either.
If you stuck them in the same team I think Hamilton would probably beat Vettel more often than not, but before he was a father it would have been a close-run thing.