Nothing ever changes in 40k.
No race actually changes anything ever. Although I would venture a guess that Orks and Nids get to be whipping boys more often than other armies along with the Guard maybe.
If someone needs to job it's usually them that get to do it.
Like all the other races though, the way it works is they don't really operate to their full potential without unusually good leadership.
This allows the player to project himself onto the setting as the really good leadership.
So like, in the Ork case, especially stupid Warbosses or mobs without actual Warbosses present are mere fodder. But the Players army is not because it's got a Badass, surprisingly cunning leader, whose triumph you vicariously experience through 40k.
But if you want an example of Orks getting out of hand, look at Armageddon. Sure that's a sttalemate, but only because resources are continually poured into it. Sometimes, the Orks make temporary headway through the million monkeys hammering at a type writer strategem of sheer luck and persistence.
Either way the whole system is a massive bleeding sore and drain on resources that could be used elsewhere, both from local sources, and from other places diverted to Armageddon.