What if we leave out of the equation electricity and cooling costs and just account only for the cost of new miners,than if you add each month for example an s9 bought from the profits of previous months than you will make more btc in the long run instead of just waiting for your miners to become obsolete and than buy new ones.
In theory I guess yes...but remember you're using more and more miners in order to make the same amount of BTC. Of course if electricity was "free" in your scenario, I'd load up with as many miners as I could get my hands on.