I get where your coming from, and I agree you can use this as an accurate way of seeing how many people have a game but have never played it. However, this does not work for Stellaris because of the Ironman mode mechanic and the fact that there are no "non-gameplay" achievements, such as switching a background colour for your empire achievement etc. All achievements are related to in-game events, and you can only access those through Ironman mode. Correct me if I am wrong, I have not checked the available achievements form some time.