JOUY31 is, as always, 100% correct on the French issues. The French emigration booth is rarely manned, IIRC.

It is just that anyone flying into the Swiss sector of GVA, even from ZRH or BSL, must go through Swiss immigration and customs which, fortunately, are hassle-free in the vast majority of cases. The minority might consider taking the train, which most people do anyway for domestic trips