You are underestimating poison procs, and it is not a 1.5AP loss but a 1AP loss, I do agree that the 3 stam is useless but id take faster poison procs over 1AP anyday, maybe if you don't have enough AP but for me I have the AP I just need the sticking power, and again if it was -2agi i'd use Screwdriver for sure, but for -1agi i'd take the constant poison procs.
PS Not trying to argue with you, I have both and I do switch every so often, but it's a question of being so close to being the same in dmg that its just preferance, just like double ele vs ele + dancing steel. I use both and switch off every so often.