Mekong56 is correct, fine tuning the azimuth affects the channel SEPARATION, not the channel BALANCE. Unless of course, we're talking about something like a tilt of 20 degrees . . .
Provided that there are no problems with connections and wiring (quite possible after a cartridge installation), or a problem downstream (verify by swapping phono output leads left for right), then the mismatch is indeed the cartridge. In fact, channel balance is a very typical cartridge specification . . . precisely because it is the component which usually determines it.