I think a ferengi megacorp is impossibel unless the workers are from offworld. Ferengi lack the discipline to keep a megacorp together.
And that's why they don't work as serious villains. If the Fererngi Alliance was supposed to be a commentary about a nightmarish version of capitalism that has gone out control, having the Ferengi have so little impulse control they could never form a megacorp doesn't work. It renders them silly rather then scary and fails both political commentary and presenting menacing villains.