But their purpose wasn't to be the villain the way the Klingons were. Everything doesn't have to be large scale. They would never be large scale villains because they need the non Ferengi races to leech off of and exploit.
But if they can't do anything large scale then they aren't very menacing villains, are they? Every other civilization they can organize themselves well comes off as more threatening then the Ferengi who have no long term planning abilities. The schemes of the Cardassians and Romulans seem far dangerous then the Ferengi who will just get distracted by anything shiny. In the world of intergalactic relations, the civilization with no impulse control will be the loser.
The Ferengi frankly should have different races working for them when they first appeared, they should have had someone else be the muscle for them. They don't look very menacing, they are merchants not soldiers, so they should hire others to fight for them. They should have been schemers, not fighters, but they weren't very good scheming in TNG. But they were presented as greedy children in early TNG, so they didn't seem to be smart enough to come up with a good scheme or hire a stronger race to be their muscle, that's why they were demoted to comic relief.
I don't think you can have a civilization be commentary on the dark side of capitalism and not have something as important to modern capitalism as corporations are.