It's a little relevant, they aren't capturing any more than the 17% of the premiums (and they aren't capturing all of it as profit, they do provide some necessary administration).
In contrast, the Medicare program spends less than 2% of its budget on administrative costs.
In a functioning market they would face competition for customers and try to lower premiums (and so try to lower costs). In our system they seem to look at provider prices in a region and decide if they can profit there or not (and in the case of non profits, if they can operate without losing money).