The government subsidizes ACA plans for many participants. That was partly meant to soften the impact of requiring coverage for pre-existing conditions. And then there is/was the individual mandate, to get everyone to contribute even if they were currently healthy. The ACA also imposed a tax on high earners (IIRC, >=200K, not sure if it is inflation adjusted) to fund the subsidies, and it cut spending on Medicare Advantage, which costs the government more than the other medicare plans.
That being said, I'm not disagreeing that costs went up after the ACA more than they would have, but, IMO that was just insurers/providers raising prices because they could.
There's no evidence that costs went up after the ACA more than they would have, and, in particular, costs grew significantly faster under Bush than they have at any point after the ACA. I'm not sure I understand why we're supposed to give credence to HN-style first-principles analysis of why insurance costs should have increased; in particular, most employer-provided health plans already complied with the ACA's coverage requirements. The data simply doesn't back these arguments up.
That being said, I'm not disagreeing that costs went up after the ACA more than they would have, but, IMO that was just insurers/providers raising prices because they could.