PTA gives 40 damage at level 1. Electrocute gives 30.
PTA also makes you "vulnerable", increasing all further damage by 8-12%, Electrocute just adds some extra damage from scalings. So question here, why would a ranged champion ever go for Electrocute over PTA if they had the choice? It's like a BETTER Electrocute for ranged champions. I think these two runes need to be adjusted(the 40-180 damage removed from PTA, Electrocute slightly harder to proc) personally.
In my experience people just 3 hit proc PTA and back off, which is the exact same gameplay pattern with electrocute.