When you are alternately throwing the weight of the car sideways in speed, how do you expect it to maintain rear traction. I am no expert on RWD but you are lucky you were driving an FWD during your test that has an inherent trait to straight out itself in an event of rear traction loss (Provided- the front wheels are compensated in the right direction).
I am assuming the reference of an XLI is due to the fact that its notorious for early grip loss in sudden brakes. If thats the case, possibly the XLi allows more camber compensation on rear wheels when weight is shifted (Sideways- Not forward). Or perhaps, due to its softer and thus relatively unpredictable suspension, you could not test it to its limits.
Stay safe. Drive safe. These vehicles are not for such road tests.