> ACA was predicated on studies like this, to no avail

ACA was also predicated on broad participation. As with all insurance, the bigger the pool, the lower the premium. Insurance of any kind is primarily a risk arbitrage business and fundamentally relies on the presence of low risk consumers. ACA was designed with this in mind and made participation in the insurance pool mandatory(whether via the public marketplace, or via private).

Unfortunately for the ACA, the individual mandate was removed in 2017 via Trump's Tax Cuts and Jobs Act, which reduced the penalty to $0, while leaving intact the ban on denials based on preexisting conditions(on it's own a good thing). The elimination of the federal tax penalty caused health insurance premiums on the ACA individual marketplace to increase by an estimated 10% annually, as younger and healthier individuals dropped coverage and left behind a sicker, more expensive risk pool.

So, while it's fair to criticize the ACA, you simply can't expect a law to work if it's intentionally altered to engineer the worst case scenario specifically.

Here's the overall timeline

* March 23, 2010: President Barack Obama signs the ACA into law, establishing the individual mandate and its future financial penalties.

* June 28, 2012: The Supreme Court upholds the individual mandate's financial penalty, ruling it a valid exercise of Congress’s taxing power.

December 22, 2017: The TCJA sets the individual mandate penalty to $0. Lawmakers attached the repeal to a major federal tax overhaul package and used the budget reconciliation process that allowed the Senate to pass the measure with a simple majority vote, avoiding a filibuster.

January 1, 2019: The tax penalty officially drops to $0 nationwide, effectively eliminating the financial pressure to participate.