I wasn't able to edit my original post, so here's the correction...
All things being equal, yes, stiffer front and softer rear will add a little oversteerUNDERsteer, theoretically. However, by lowering the car a bit, you get more camber. And as you mentioned, the sways can work that so it's more balanced.
I felt that overall the whole package was a huge improvement over stock.
I find it fascinating that all of the aftermarket suspension setups seem to increase the roll stiffness to the front, which then increases understeer, if I'm reading this correctly. I already feel like it understeers too much as it is. Unless they are assuming that you're pairing up the suspension with some really stiff anti-sways, and that you'll use the sways to adjust the roll stiffness back to the rear to make it more neutral...
Or, maybe they just figure if you're going the performance suspension route, you need the added "safety" of more understeer
It's not turn-in understeer that I'm having a problem with, either, it's understeer from the apex to the exit, especially when uphill.
Turn-in is actually really good. Much better than the WRX that we have as well. It plows badly at turn-in, until it rolls over onto the outside wheels, and then it really hooks up and will gladly 4-wheel drift out with just a hair more in the front than the rear, a bobble of the throttle and it will step out the rear. Pretty much lots of throttle keeps it happy in the turns (unless you spool up and full boost between apex and exit, then it gets interesting in a hurry).
I wish the Z had more of the late-turn handling of the wrx, and kept the turn-in response it has, and I plan on working on the WRX to improve turn-in. It's definitely getting some new sways soon, as well.