Snap oversteer just comes without warning, there is no "gets a little out". Grip, grip, slide too fast to recover, no progressive warning. There's a lot more than just a single trailing arm bushing that causes lack of progressive breakaway though, it's a combination of stiff stuff. If you have stiff coilovers, sway bar, and pretty much all of your bushings are hard, you'll have problems. Make everything unyielding and you'll have no compliance left to keep enough grip. Part of this is also lowering, trailing arm geometry doesn't really take well to being lowered because the roll center of the car changes in the back.