Eyeballing this CDC death chart [1], non-accidental deaths from ages 5-44 add up to less than 30,000 per year. Most of those are cancer and heart disease deaths in the later ages. The US health system is not necessarily worse than peer health systems at dealing with such issues, and in any case, the health system can only do so much about them, because there are public health issues upstream like obesity.
But even if you magically completely wiped out those deaths only in the US and not in peer countries - which could never come even close to happening - it wouldn't do more than close half of the 60,000 gap I pointed out in my previous post. A gap caused mainly by accidental deaths (and suicide).
All this is just putting numbers to the basic, commonsense facts we know about mortality in the young: they don't die in the hospital, so making the hospital better doesn't do much to fix their mortality. And reducing the mortality of the young is the main thing needed to bridge the gap between US and peer countries, as I explained in a sibling comment.
[1] https://www.cdc.gov/injury/wisqars/pdf/leading_causes_of_dea...