LFS2,  Petain's control over France was far more complicated than you claim: 
https://en.wikipedia.org/wiki/Philippe_Pétain
He was chosen to head the French government during that chaotic period when the French army was collapsing and the Germans were sweeping across France. 
Petain then moved his government to Bordeaux, and he eventually participated in negotiating France's defeat with the Germans.  This allowed France to form their infamous pro-German Vichy government  under Petain in the unoccupied region of France.
As you say, he was convicted of treason for having overthrown the French Republic and establishing his semi-Fascistic government.  He was eventually commuted as an Old Hero.
Point being, he stood for similar values to LePens'-- a strong, nationalistic France with shades of authoritarianism--something many French people seem to be yearning for with LePen.  There's a reason why virtually all other French parties are  uniting against the threat of a  LePen victory.