My understanding was healthcare.gov was a failure until a small team took over and redid the full thing in ruby on rails just to get it all working, and then later it was ported to something more performant. Is that true?
No. The original site was a Java/J2EE application, and that's what the small team you refer to helped to stabilize on the rescue. We got it working well enough to make it through that first enrollment year. There was no rewrite into Ruby on Rails.
Later, and over time, key components of HealthCare.gov were redesigned and rebuilt. Rails was used for some, Go for others, and there is still some Java from the original design.
