Yeah, even if you just arbitrarily chop 20-30% off of US healthcare costs--which aren't just from the pockets of fairly low margin insurance companies, the money still needs to come from somewhere. So maybe a random individual can get a decent insurance plan for $5K/year with a family plan something north of $10K without a company paying. I expect a lot of people would still not find that reasonable and would want someone else to pay for it.
But ACA did what it could with the political compromises that had to be made at the time. It provided out of pocket maximums, maximum age rating factor (age 64 only pays 3x age 21), and required coverage for all applicants (removing risk of disqualification from pre existing condition).
It is unfortunate the mandate was repealed and state level participation in functioning marketplaces was politically hampered.