Zilean is not useless at all lol. Actually, there are no useless champions, if you're good at playing, for example, Urgot, then you can't be useless. Some champions are weaker than average and people just call them useless which is just wrong. Imo, there are no useless champions.
Yea Zil is good at mid but late game he fall down same like urgot they become completily useless if not good snowball early game