I've just been on contact with Sequential about the same thing. Support says that, yes, the difference in oscillator levels is within tolerance. I didn't get the word about it being an intentional part of the design, but if so, I can dig it.
I only noticed the difference in levels once I started playing around with the "James Meek GS" trick, i.e. not pumping the oscs full volume all the time. I wonder if this has to do with me never quite getting the detuned oscs to blur the way they do so naturally on the P5. Anyway, it's not a life/death issue for me, and I now know to bump osc 1 a bit louder than osc 2 when I need them balanced.