> Lifespan has also increased with decreased gut biome diversity.
Life expectancy increase is mostly a factor of decreased death at birth or in early years. You dont see an exponential increase of 100 years old. People die at about the same age as before, give or take.
Parent's point is that you can draw a correlation to a beneficial factor without examination of whether causation exists just as easily.
You correctly identify that it is unlikely your lifespan is increasing because the average gut bacteria diversity is decreasing, more likely they are simple correlated.
This is not true. An average adult lives longer still just not by that much. Whole bunch of deadly diseases or injuries are not deadly anymore. The work got safer and injuries happen significantly less often.
What did not changed is maximum longevity people have assuming they don't get sick or injured.
Neither accidents nor sicknesss are noise. Both are and especially were fairly frequent reason of death. And whether you survive them has a lot to do with both medical and social improvements.
Life expectancy increase is mostly a factor of decreased death at birth or in early years. You dont see an exponential increase of 100 years old. People die at about the same age as before, give or take.