They are just so straightforward that even knowing their counter doesnt help. They are straighforward but they also can quickly adopt to any situation. They can switch to a trash army quickly, they can quickly go for archers... I think it is just their economic bonuses. Castle bonus and forager bonus creates a perfect transitioning from scout rush to castle drop.
My elo is around 800 and people here before said civ doesnt matter at that elo but nothing could further be from truth. If that was the truth I wouldnt be getting defeated every single time by franks even though my win/lose ratio is around %50. No matter what strategy I use or what civ I pick. Its like even if you counter their strategy initially, they will always have an edge regardless.
I know it is the noob civilization, they become less of a problem in higher elos but holy hell when I face Franks it is like I play against someone 50 elo higher.