Who is in charge of negotiating for this pool? Just as an example between 2017-2018 the average silver plan went up 32% and the average gold plan 20%, who the hell negotiated that?
At least with the employer provided insurance the employer is negotiating, and you know who that is and you know they have a self-interest in keeping costs down.
The price of insurance jumped massively every year from the start of Obamacare to 2018. The fact that this has apparently mostly stopped now is the unusual thing; 2017-18 was a pretty typical year despite Trump's meddling. The article you linked suggests that this is because insurers have finally increases the cost of insurance to be in line with how much it actually costs them.
Sure the employer negotiates the plan, but they are not negotiating on behalf of their employees, they are negotiating based on how much the employer is willing to spend. When the squeeze happens, the employer pays the same amount for a slimmer plan and the employees pay more in the form of wages and deductibles.
At least with the employer provided insurance the employer is negotiating, and you know who that is and you know they have a self-interest in keeping costs down.