I don't want to get into the history books but you sure have neglected a few facts there..
1- Real Madrid started to dominate in 1953 till a few years after Franco was gone (You wouldn't expect Franco's effect to die out immediately when he's gone, like you don't expect Man City now to suddenly go back to fighting for mid-table places if Sheikh Mansour is gone now!). They won 18 of their 31 league titles in this era (for Barcelona's 7)..
2- During these years Real Madrid was sent every year to compete in the European competitions even if they didn't win the league.. Spain sent only one team at the time..
3- It was not only political pressure, Di Stephano was not allowed to join Barcelona (which was his intention and the deal was even done) the year before he joined Real Madrid. He was only allowed to join Real Madrid, a year after..
4- When a player like Cruyff says (in the 1970s) that he chose Barça over Real Madrid because he could not play for a club associated with Franco, publicly in the media, that gives you an impression about how well-known that fact was at the time..
Franco wasn't a football fan, but he hated Barcelona (Catalunya), and because Barcelona loved football he used it whenever he can as a tool to punish them..
Anyway, like I said, I don't wanna get into the history books (not at all

), but there is enough in it for me to hate Real Madrid.