I do not think this is entirely accurate. Lung cancer in smokers hits unusually young people because, well, they are smokers. Heart disease is a disease of old age and accelerating it somewhat through an unhealthy diet would have complex effects. However, making matters even more complicated, ultraprocessed foods also promote cancers and obesity—the latter is definitely a huge healthcare burden which does not kill people immediately.
This is hard to model since there can be a shift from a disease that kills slowly to one that kills quickly and early (dementia to lung cancer), but you can have also the opposite shift (e.g. from a non-disease state to chronic COPD and frailty preceding death).
All we can say for sure is that the harmful effects of smoking and junk food diets may be offset to some extent. More so for smoking than junk food.
Either way, it would appear the consensus is that “in high-income countries, lifetime health care costs are greater for smokers than for non-smokers, even after accounting for the shorter lives of smokers”
https://www.tobaccoinaustralia.org.au/chapter-17-economics/17-2-the-costs-of-smoking
Does not make that much intuitive sense to me because there are a lot of random mutations happening. If the first dose first (or first dose only) strategy reduces the size of the whole SARS-CoV-2 viriome, there will be fewer viruses and less genetic variation in total. More infections in total means more genetic diversity. More infections means that a vaccinated person will be exposed to more sources of infection, more virions, more different genomes over time, thus also increasing the likelihood of mutants able to escape the immunologic response.