My reply comes a bit late since I managed to write a long comment without clicking send and only noticed this now. I will address the errors I see in the TL;DR summary from the POV of a semi-professional biogerontologist:
The disease-based approach to aging this seems to favour is useful, but limited. In fact, if you genuinely want to extend both lifespan and healthspan this excessive focus on the disease-based approach would be inefficient because is inconsistent with everything we know about aging. I would go as far as to say that the disease-based approach may be actively harmful because it takes away resources from genuine aging research.
While aging probably has thousands of causes, or even more*, this does not preclude the existence of major causes that limit lifespan in the near term. This idea has been popularized by Aubrey de Grey a long time ago and now has reached the scientific mainstream with an emerging consensus about the Hallmarks of Aging (several key pathways and sequelae of aging). We also know that this view is decently well supported in mice and have known so since the late 1990s when Holly Brown-Borg and Andrzej Bartke introduced the Ames dwarf mouse to gerontology. If aging was strictly multifactorial and polygenetic there would be no hope to identify single genes that lead to pronounced lifespan extension, as they did with the long-lived Ames mouse, which is long-lived because of an underdeveloped pituitary and reduced growth hormone levels. This means one simple change to a single pathway can extend lifespan.
Of course, I am biased, since as a biogerontologist I think the biggest gains are to be had from targeting aging directly, although we can have a discussion how well the mouse data translates to humans. (Not well, IMHO, but it is the best we have.)
Sizable lifespan extension we have seen in mice has come, without exception, from interventions that target aging directly through the above discussed “hallmarks”. Just to give three famous examples of life extending treatments: We have Rapamycin, an inhibitor of the mTOR pathway, that became a plausible candidate after this pathway had been implicated in the aging of yeast. Then we have caloric restriction, which was discovered by accident and not by the disease-based approach, but is now known to target a global pathway that promotes tissue maintenance under nutrient stress. Finally, we also have senolytics, drugs that were developed to kill senescent cells, that had been linked with aging after decades of biogerontologic research.
In contrast, drugs like Aspirin, Simvastatin, Enalapril and many others were tested in mice with no clear biogerontologic rationale behind them and predictably failed to extend lifespan, even though they are obviously amazing from a disease-prevention point of view.
However, I do agree that biogerontology depends on the existence of a strong biomedical ecosystem. Rapamycin was initially discovered as an immunosuppressant and if not for that, it would have taken longer to find inhibitors of the mTOR pathway (but eventually it would have happened by standard medicinal chemistry). Working in the 1930s Clive McKay, the discoverer of caloric restriction, was perhaps more interested in the basic biology of starvation and malnutrition than finding treatments for aging, etc.
Nothing about age-related multimorbidity makes sense if it not viewed through the lens of biogerontology.
Notes* for example, you may be able to get 10-30% of lifespan extension by targeting the top 10 causes of aging, then eventually as you want to extend lifespan more and more, other causes of aging would take the spotlight