Pardon my utter ignorance/disbelief - are opioids killing/debilitating that many people to get this result?
Those are the leading causes of death, but not the leading causes of the recent decline in life expectancy (heart disease has not contributed to a dramatic decrease is life expectancy).
The recent decrease is due to deaths from drug overdoses. They aren't the leading cause of death, but they have caused the life expectancy to decrease in the last few years.
The reason it disproportionately impacts life expectancy, is because a lot of the people overdosing are young.
If you suddenly have 250,000 people under 40 years of age overdosing over five years, you're going to see it in the life expectancy numbers even if your population is 320m. The small increases you'd expect to see in life expectancy year by year otherwise, will evaporate.
To get a picture of the overall health impact (non overdose deaths), one would need to look at how many additional addicts the opioid explosion has caused (eg in the last 10-15 years), study the health impact over time on those people, and so on.
A net change of 0.4 years is not insignificant, but I think you're ignoring the elephant in the room (China's rapid development in the last decade).
On another vein, I'd argue overdosing on drugs is an intrinsic part to the American experience.
And what does it have to with China "dumping" it? FDA approved Fetanyl and American doctors are prescribing it. It's on us to reign it in.