If I die at 90 of a heart attack havjng maintained the ability to live independently up until then, I’d take that as a massive win compared to my relatives suffering through a decade of me with worsening dementia.
Cardiovascular diseases are huge risk factors for dementia, so if your goal is to avoid dementia you should try to have a healthy cardiovascular system.
If health science was as simple as health outcomes are proportional to one or two measurement percentiles, sure. But that's hardly true. Health is a lot more complex than that and the disease risk cannot be quantified by a small number of parameters
