San Fran for instance had nearly double the passing yards than rushing yards this season, yet they had slightly more rush attempts than pass attempts and were the #2 rushing team in the league (and only 13th in the league in passing).
A balanced offense is not one that has similar rushing and passing yards (that would be an unbalanced offense likely resulting from one of two things: either having a tremendous rush attack with very high yds per rush attempt or a poor pass offense with very low yds per pass attempt). A balanced offense is one that has similar rushing and passing attempts, and specifically designed rush attempts by RBs (with the rare exception being the teams who have legitimate running threats at QB and run lots of designed runs for the QB).
If balanced "and" successful, an offense should average around 4 yds or more per rush attempt while around 8 yds or more per pass attempt would be expected, so yeah if a team is balanced on offense they "should" have around double the passing yds.