I didn't label him only a brigand. I compared him, si parva licet componere magnis (just to keep O'Lennaine happy) to the Haiduks and Klephts, who were brigands with political overtones. Koloktrones and Odysseus the great Greek leaders in their War of Independence are the classic example. Odysseus in particular. If one were to put Odysseus in 13th century Scotland, or Wallace in 1820s Greece, you wouldn't notice much difference. Brave, charismatic, intelligent, unscrupoulus and ruthless, for men of this sort, conflict was not a means to an end, but the end itself.
If one wishes to look at Wallace using 19th century concepts of nationalism, go right ahead.
Just remember that brigandage and revolt aren't incompatable.

"Then, after Stirling Bridge, "Wallace and ...Murray were now the de facto joint rulers of Scotland, working in the name of John Balliol, the deposed king, and the people all over Scotland rallied to them--including most churchmen and some at least of the nobility."

So, it seems reasonable to say that at this point he had progressed beyond brigandage."

Or worked on a larger scale.
I think Scotland and Northern England were probably very lucky that he didn't live to see peacetime.