The providers still hold the key to pricing. When your choice of hospitals or specialists is limited, you’re going to go with whatever insurance company they accept, or pay some exorbitant price.
The problem is that most people don't pre-shop for insurance that way, and only find out that their local provider is out of network when it's urgent that they get help.
Even if you plan it all out ahead of time, you end up in emergency surgery in an in-network hospital, with an in-network surgeon, only to find out the anesthesiologist was out-of-network. And you still owe tens of thousands of dollars out of pocket. It's a bad system all around.
The problem is that most people don't pre-shop for insurance that way, and only find out that their local provider is out of network when it's urgent that they get help.