Q: Why upgrade the whole suspension on a car that already has 1,020hp?

Because power without chassis control is wasted. The stock Plaid puts down enormous grip and weight, and the factory rubber bushings and soft geometry were not built to exploit that at the limit. This package reduces body roll, drops the center of gravity, and replaces the compliant rear links with billet arms and spherical bushings, so the car finally uses its power through a corner instead of just in a straight line.