Even when the Scots ruled the English they made a point of putting England first. Being King of Scotland was sub par and they knew it. A low populated small country of mountains and islands on the edge of the old world. Being King of England was a pretty big deal. England was important. Not really comparable with a united France, but there was no such place. Scotland, or to be more honest the other England, (the part of Scotland where all the people actually live was basically North-North England) took the world by storm in the modern era, but the medieval era was not it's time.
It's important to understand that the romantic idea of Robert the Bruce and William Wallace was written for an 18th century Scottish audience (by Burns of course) who were in mixed opposition to the United Kingdom and were looking at the American and French revolutions. The formative development of the modern Scottish identity is somewhat anti-Union and anti-English and either Radically Liberal or Jacobite Lost Cause whether it's fair or not. The modern SNP is just acting in the national character.