I remember Plato talking about the Toledo, and that as a standard car the chassis wasn't all that brilliant. So making a racing car effectively using the same base road car underneath would still have some of the flaws of the road car.
The Leon has a better basic chassis, and as a result the racing car is that much better to start with, before they start adding bits.
Now if the Vectra is as understeery as the Top Gear
video suggests, VX have their work cut-out.