Foden made a great run in behind and we were lucky the ball was at head height, if it was lower he would have had to have used his weaker right foot to play it into Aguero's path. Just roughly I'd say 30% chance maximum on most players weaker foot, maybe 70% chance on most players stronger foot of making a successful cutback. That's the difference.
Foden is a really bad example because he's actually very clean and precise with his weaker right foot as we've seen with his first time strike in the earlier rounds of the league cup and also a cushioned volley cross to the back post for Aguero against someone in the league, can't remember who on either occasion. If that's Mahrez on the right or Sterling on the left, you know in your heart of hearts that ball isn't going to be put cleanly into Aguero's path. Mahrez/Bernardo on the right would try a fancy flick and Sterling wouldn't strike it cleanly, although at least he would try.
As for your point of opposition wingers doubling up, great. That's when our fullback can make an underlapping run or move into a central midfield role to support #6 against a counter attack while also allowing the #8's more freedom to join the striker. A winger on his natural side can still get a cross in by just beating the fullback too, eliminating the effectiveness of the opposition winger doubling up.