He is, and he does - De Jong plays (when used correctly) as the deepest midfielder. Operating in a double pivot doesn't change that.
There is no 'correct' formation. A 4-2-3-1 can't be outdated (since I've started watching football anyway, there's been no changes to the laws significant enough to render any particular established shape obsolete). That's a particularly strange stance to take with your assertion that it has to be a 4-3-3 - the difference can be extremely negligible, and the former matches up perfectly against the latter. Bayern Munich were the best team in Europe playing a 4-2-3-1 a few years ago (and the winners of the last World Cup did so playing a 4-4-2, to object to the idea that that is another formation unusable in the current football world). And of course, designated formations are extremely simple descriptions of a teams shape, and can't tell you a whole lot.