Without question. The US for example had a higher life expectancy than New Zealand during the 1980s, then the US began to trail off and fall behind. Now it's ~2.7 years behind New Zealand. The US was also ahead of the UK as recently as 1983.

What changed? A few big things. Healthcare in the US became wildly expensive after the 1980s, following an extreme cost increase far beyond inflation, whereas before it was not far out of line vs other developed nations (eg share of GDP spent on healthcare; today it's commonly 2x the next closest nations on cost). And obesity exploded dramatically higher after the early to mid 1980s. Diets overloaded with sugar, carbs, high fructose corn syrup in everything, drive thrus as a routine, etc.

I do believe universal healthcare would have prevented that life expectancy gap from opening up between the US and the UK, Canada, New Zealand and Australia. Based on the expectancy increase path the US was on as recently as the early 1980s, it should be at 82-83 years now, rather than 78.x.