Been quite frequently to Paris recently and cannot confirm what you describe.
Of course there are plenty (of teenagers) wearing jeans, skater clothes, ... but on average men were not dressed worse than in other European major cities (maybe except for Milan) and certainly better than in all North American large cities, e.g. there are by far less square-toe shoes, suits which actually fit the wearer.
Regarding A&F in Paris: There is also McDonalds, Burger King & Co in Paris, but that does not mean that all food in France is now crap. By the way, the Avenue des Champs-Élysées is not the high end shopping street in Paris and largely crowded by tourists.