While I don't doubt that there's a slight temporary productivity boost, I doubt it outweighs:

1) Lost years of productivity as people die early from lung cancer (my smoker granddad ended his career early because of it, a challenging maritime career that as I understand it has an increasing shortage of workers).

2) Healthcare resources being directed towards diseases directly caused by smoking. Tax money and individual money that could've been productively invested elsewhere, plus the working hours of healthcare professionals (another field with a shortage).