The big difference between CS and CI (aside from weight), is thermal bounce. They both can be heated to very high temps without warping, but the CI has a shallow, but slower thermal bounce than CS. With CS, when you put something (relatively) cold in it, the bounce is swift and steep, but regains it's heat quickly. With CI it can take awhile to recover (for example, deep frying in CI, you can observe the bounce in the oil). CI excels at low, slow heat on a cooktop because of the shallower fluctuations in heat. The CS excels at high heat operations like searing and saute, because it gets hot, and bounces back quickly. CS pans are excellent for getting a crisp crust on a steak for example. Both can be seasoned to near nonstick level of smoothness.
Just different tools for different tasks.