I don't take it as a history lesson, but being that it is supposed to represent real people and real events (on some level, of course you allow for some degree of looseness in a film) the fact that it is woefully inaccuate does seriously detract from the film as a whole. It is supposed to be a depiction of a real period of history. And no, they didn't use facepaint. That is a minor complaint; that was the point though, it was one of many little things which are inaccurate which detract from the film for me (the costumes/kilts, the paint, there being no bridge at the Battle of Stirling Bridge, even the fucking date being wrong - when combined with the complete bullshit that is the portrayal of Wallace, and the plot of the film in general.
Each to their own of course.