Saidur, compared to other driving games, Forza is a lot closer to real life physics. Therefore you just HAVE to come in slow, start downshifting, and slowly turn the front wheels. Avoid going to full lock on the analog stick, unless it's a really sharp turn or hairpin. Midway during a turn, you might need to feather the throttle or intermittently tap it just a little, to keep the nose where you want it (isn't very helpful regarding FWD naturally), and go out fast, practically as if you're slingshotting your way out of the corner.
Yes, FM has had this assist since FM3: the controller will not allow you to turn the front wheels past a certain point unless you slow down further. I think they're trying to simulate steering wheel mechanics of an actual car on a controller, but I find this annoying too. The game should at least have a setting to adjust speed sensitive steering as well as steering speed.
BTW, this issue has been discussed at length in both the FM4 and 5 sections on forzamotorsport.net.
This assist will always be there no matter what set up you have, assists off or not, SIM steering or not, whatever deadzone settings you have, you cannot change the way the controller registers your inputs, based on speed. So the best we can do here is to adjust our driving style accordingly. It's good in a way, as it forces you to be a better precision driver.
If you're still finding it cumbersome, you might as well get a gaming wheel. That way, you'll have almost complete freedom and control over the front wheels.
Edit: read the CVG review. Not sure if the other websites are Forza-biased or not, but on every major site, it's gotten an 8/10 score or higher. Strange. I suppose I will decide for myself if/when I get to own the game.