mild steel flat bar and spring steel are still very different. i don't buy your theory. thats due to fulcrum action (leverage) same as using a 4 foot pipe on a 15inch flex bar springs are different. different in design and also metalurgy.

why are boy racers with cut coils spotable from a mile away ? because they handle much like a jelly bean!

Mild steel and spring steel both perform elastically with a linear increase in resistance up to a certain point.

If you use your hand with no levers to twist the flat bar, there is no leverage. As i say coils twist when compressed, and this is the way they store energy.

You can make a coil from mild steel and it will still perform like a coil, up to a certain point, depending on the design. Spring steel coils on cars are often designed so they can be compressed till bound, without being overstressed. A mild steel coil could also be designed to be this way.

yeah, you can see them bouncing, correct?
The reason they are bouncing is because the spring is stiffer and the crap shocks they have can no longer exert enough damping on the spring to stop it bouncing.

It's true that most people that cut coils are doing it because it's cheaper, and at best they may also fit cheap standard length h/d shocks, and because they are standard length and they didn't renew the bump stops the shocks may bottom out and stop working properly anyway. I speak against this kind of behaviour.

But that doesn't mean coils can't be cut to professional standards for good reasons and appropriate shocks fitted. For most people buying lowered coils is the better option though.