#1 - eventually you'll qualify for medicare. The "Pay for healthcare" portion of the portfolio doesn't have to last forever.
#2 - unsubsidized once you're retired is a pretty big assumption - once you're in the withdrawal phase, you can control your income to a greater degree.
#3 - that silver plan premium might be artificially high. Subsidies based on "2nd most expensive silver level plan" have led the silver plans to increase in price faster than the other plans. For example, in my county, the average premium for an unsubsidized silver plan is actually a bit higher than for a gold plan. Insurers and state insurance boards have set prices to maximize the federal dollars flowing in.
But overall, yeah healthcare is crazy expensive in the US. It has been for a long time. One thing the ACA has done is make more people aware of that. Before, many were sheltered from the cost of insurance by employer subsidies, or on the individual market by the fact there was no guaranteed issuance - fairly easy to keep insurance cheap if you only have to write policies for healthy people.