User blog comment:RoznosicielCiast/Is Siphoning Strike too strong?/@comment-4952847-20131105015328

Siphoning Strike is strong, crazily strong, but not overpoweredly so, because it's on Nasus.

The biggest holdback to Nasus is his kit lacking innate mobility, only having one single target CC to really make use of this skill, his lack of ability to actually reliably farm, as well as Siphoning Strike acting as the only reliable damage output.

The skill on its own is too strong, so it can't be slapped onto just anyone. It's not the perfect synergy to Nasus's kit but it can't be used on anyone else and Nasus won't be playable without it.