I am of the opinion that Joan of Arc, an "amateur" general, started France on the road to winning the war because she understood something that the "professionals" did not; that is, that the French army was fundamentally better despite the earlier English victories, and that "all" that was needed to win was for France to fight the right battles.
My understanding is that the French had better artillery, a multiple of the number of English troops, and as a result, a wider range of weaponry for "combined arms" operations. The English had superiority in only one area, the long bow, which they had used to devastating effect at Crecy, Poitiers, and Agincourt. England's alliance with Burgundy mitigated, but did not eliminate, the French advantages.
The above is the general sense that I have, but my knowledge its a bit sketchy. Can anyone describe the French vs. English advantages with a greater degree of "granularity?" And if so, is it fair to say that Joan's gift was realizing that the French could win, under any reasonably competent "combined arms" commander (which she had behind her) even more than understanding how they could win? That is, of course, if the French could avoid battles and situations where the English long bow would show to advantage.