Version 3.7.0
Webbed Shot
Cooldown removed for early levels
No longer considered an Attack Modifier
and im 100% sure viper in Dota 1 had also one. You are right though, in Dota 2 right now Viper also has a 0 cooldown on it, but its a whole different meta with the additional skill tree and Heroes having generally more hp and less burst. [e. g. mirana(aka. valk) can leap 3 times in a row - this would be broken in hon]
I agree that Arachna got nerfed, but imo the nerf was being in the wrong direction because that mentioned 0 cooldown was the broken part of