He's definitely up there, and one can make a case for Steyn being better than Waqar in Tests, but better than Wasim? Not in my opinion - at least not yet.
In fact I'd actually wait until the end of his career to even say he's better than Waqar, let alone Wasim.
My reasons for that is that Steyn has played more than half of his career games at home, which is not the case with Waqar/Wasim. Additionally, career longevity is another thing to consider when comparing him with Wasim (though this factor doesn't help Waqar).
That said, Steyn is brutal. A total beast, and a treat to watch. He's been bullying batsmen pretty much everywhere, whereas Waqar seemed to have struggled in India whereas Wasim didn't find bowling in South Africa too easy (albeit a very small sample size in both cases). Steyn's SR also speaks volumes about his class.
At the moment, I would say he's definitely up there with the legends, but not quite better than Wasim/Waqar just yet. Needs to keep this up for a few more Tests, and needs a few more games outside of SA. By the end of his career, though, it'll probably be something like Wasim > Steyn > Waqar, IMO.
To say that Steyn is 'comfortably' than Wasim/Waqar in Tests is delusional.