To be fair both Kubrick and Tarkovsky probably felt dwarfed by the likes of Vertov, Eisenstein, or even Chaplin. Specifically in terms of pushing the envelope. These were different times with different envelopes.

Villeneuve innovates in a different space, maybe not as philosophical as Tartovsky, and not as symbolic as Fellini... but I don't think that language and that storytelling would work nowadays anyway. There is also Nolan with his very sophisticated world building. Yes it's all pretty mainstream, but so was Kubrick and Tarkovsky (at least in the USSR).

You mention Tarantino (which I personally don't like), but there are many lesser known directors from the 90s-2000s with a fantastic filmography. Kim Ki-Duk and Noel Gaspar come to mind. The world of cinema has not stalled, maybe we need to look outside of Hollywood more eagerly (but then again, neither Fellini nor Tarkovsky where Hollywood).