The people who get screwed the hardest are the underinsured (in all cases) and those who have high-deductible plans with coinsurance and HSAs (and have some acute issue).
I work in radiology and entered a few common procedures I see a lot in our data on https://turquoise.health/ (also linked in the Twitter thread). Then I entered information for our own HDHP+HSA plan. Guess what, having insurance costs you 40-60% more if it's an acute issue. So if you're healthy, you have zero incentive to use your insurance if you suddenly need a CT of something. The rub of course is if you pay cash, it doesn't count toward your multi-thousand dollar yearly deductible, so if it turns out to be a chronic issue you just shot yourself in the foot. But if it doesn't, you just burned thousands by using your insurance when you didn't have to.
It's a complicated issue and anyone who says they have the solution, including "just make it free / just have the government pay for everything," is either being disingenuous or doesn't understand the problem. As was stated in the Twitter thread, running a hospital 24/7 is astronomically expensive. Everyone has their finger in the pot trying to get paid for their services in a world of increasingly small reimbursements. Attending physicians as resident-run hospitals will sleep overnight while getting paid literally half a million dollars a year. Insurance companies will just decide not to pay something and will spend years in court to defend their right to pay whatever they want, down to and including $0. Vendors will charge tens of millions of dollars to implement monolithic thick-client applications where everything is so configuration-heavy that you literally can't have a test environment because it won't match. Interoperability is managed by a text-based standard named HL7 that if you're not familiar with, will make you rip your hair out. The standard itself is ignored by every organization who ends up with their own flavor, so every app needs to be configured to support nearly any value in nearly any field. Hospital IT is staffed by people making $40k/yr who don't understand modern computing, and run by executives with no technical background.
Every single entity and company involved in healthcare is complicit in the end result, which is skyrocketing patient costs with at best no change in patient care or patient outcomes.