I would not say light Infantry sux. Ex. C'tis light Infantry armed with spear, javalin and shield can be quiet useful. An unit with 30 or more with light infantry can block off a heavy cavalry when its charging.
The light infantry can take out the heavy infantry if it gets its chance to hurling the javalins, the same goes against archers.
That's my experience with C'tis light infantry plus they are cheap
Thilock