To a degree your right. You could put on braces and thicker antiroll bars with stock sus and it would be stiff.
But stiffness and shock absorption are 2 completely different things. the ride quality would be better with Shocks and springs package than just springs. As someone said Teins would work better on track than a country road which I looking for!
Teins are rock hard compared koni which i wouldn't want. Thats the point I'm trying to make and find out what would be best for me!