Static and Kinetic friction is variable with all materials... Silk and sandpaper?
Instructors are giving you good solid advice at a starting point. You have a nice car, and you should be prepared to protect it and yourself and me if I'm on the track too.
There is always a point that the tire (any tire) will have grip to no grip and lose control. The R tires have much more grip, to a point, which will be a higher cornering speed, so when it goes, you go with it. Its very much akin to surface conditions and tire quality..ie snow, rain etc...hence the invention of anti-lock brakes that maximize the tire grip in adverse conditions. Poor tires squeal at the Timmy's drive-through, so you know what the limits are.
The problem here is Mosport can be very unforgiving and you woudn't want your car backed into the wall at turn 1!