Please take a look at Press the attack :
Passive: Basic attacks against enemy champions apply stacks for 4 seconds. Attacking a new target removes all stacks from the previous target. Applying 3 stacks to a target deals 40 − 180 (based on level) bonus Attack damage Ability power Adaptive damage and makes them Exposed for 6 seconds, causing them to take 8% − 12% (based on level) increased damage from all subsequent sources (except from true damage).
And then compare it to Electrocute :
Passive: Basic attacks and abilities generate stacks on enemy champions hit, up to one per attack or cast. Applying 3 stacks to a target within a 3 second period causes them to be struck by lightning, dealing them 30 − 180 (based on level) (+ 40% bonus AD) (+ 25% AP) Attack damageAbility power Adaptive damage.
25 − 20 (based on level) seconds
Basically press the attack does more dmg than Electrocute on low level and almost has a non-existant cooldown. Considering how easy it is for him to proc that rune, it's no wonder how easily he can win quick squirmishes.
All it takes to cut down on Lucian's power is to cut down dmg from Press the attack (LOWER BASE DMG, LEAVE THE MAX DMG UNTOUCHED). He is one of the only Range champion that takes Press the attack as its main rune and has been a clear favorite in bot lane for his great burst, dashes and sustain.