An under discussed downside of market-based healthcare systems like the ACA is that Medical Loss Ratio rules (limiting insurers profits/admin to 20%) incentivize insurers to not care about controlling rising healthcare unit costs.

By restricting what share of the pie they can take in profit, they end up letting the pie get bigger so they can make more profit in absolute terms. But one of their main jobs (especially important in the US context) is supposed to be controlling costs.