someone help me out with my xerath play

http://i.imgur.com/epxe6k3.png

http://i.imgur.com/OWayG6u.png

for whatever reason.... my xerath play is not cutting it for the team.

i always feel like im a source of damage, but because im not setting people up or 100-0ing im not an effective mid laner, like i have a ton of success on vel koz who does basically the same job, except hes combo is much more potent and reliable. its the same thing on ziggs another 4 skill shot champ.

but my xerath damage and cs values are all very similar to skill skill shot based champs.

i know im hitting targets but for whatever reason when i play xerath we just lose.

its not landing skill shots vs not landing skill shots. otherwise id be garbo on velkoz/ziggs.