alt Hacker NewsI am not in one, but from what I heard the answer is sort of. You usually end up with two corrupt power hierarchies fighting each other - the corporation and the union. That's better than just being subject to the whims of one that's aligned against you, but it's not ideal.
A good place to see the difference is an Airline. Strong unions, like the pilot's union...makes for very different outcomes for them versus the salaried/non-union HDQ type workers.
But yes you're right it really depends on power dynamics.