Please, stop repeating russian propaganda. They wanted to control and reconquer their former imperial colonies. Their claimed Casus Belli were just lame excuses, not actual reasons.
In practice, light gathering correlates to F-stop quite well on most normal modern lenses, transmission losses are very low. The main exceptions are deliberately apodized lenses, which have considerably transmission losses wide open.
For the rest - yeah, f# is just one of important specifications.