Hold on

10.9 Developer Preview 2 is buggy. We can't draw a conclusion until we see a GM. Did you test it with Lion and ML?
Note: I have one rMBP that's for my own personal use, and I have access to one 2012 cMBP 15" and a 2010 cMBP 17" that are my colleagues'. Henceforth, whenever I write "cMBP", that means it's the 15" 2012 model. And if I wanna refer to the 17", I'd just write "cMBP 17".
In Lion, rMBP is significantly worse than cMBP. But it's about equal to cMBP 17. cMBP 17 is significantly worse than when it was in Snow Leopard.
In Mountain Lion, rMBP is closer to cMBP, and it's actually better than cMBP 17.
In 10.9 DP2, rMBP is exactly the same as cMBP performance-wise, and is way ahead of cMBP 17, even though cMBP 17 also sees a boost that makes it about equal to rMBP in Mountain Lion.
Bugs in 10.9 DP2 be damned. They just cause crashes and oddities. They don't and shouldn't affect interface performance.
Seriously, 10.9 is a lot smoother than Mountain Lion in pretty much everything. Granted, I'll give you that scaled resolutions on rMBP are still not up to par, but "Best For Retina" is significantly smoother.
rMBP only "lags" if you compare it to the same generation hardware on cMBP, but when you compare it to another Mac that's made before 2011, it's still a huge leap in performance and smoothness.