Sure, but there's usually plenty of other tradeoffs in any system of notable complexity. This is certainly a system of notable complexity. We may find that there is mental degradation that's not covered by this. We may discover that cancer is practically unavoidable if you live long enough, and the problem compounds even further with age than we can anticipate now. There's never just one lever being pulled in isolation.
I mean, if you gain +20 years of longevity to most of the body, but not to mind? That's still 20 extra years of lifespan if you're lucky. And if you aren't, it's still better health in general, until your mind goes.
There are old people who remain lucid and active well into their nineties, not getting dementia or cancer - through some combination of good luck, good genes and good lifestyle choices. They live a good life - until a stroke cripples them, or the heart fails them, or a very mundane illness like flu puts them in bed and they never quite recover from it. If that couldn't happen to them, how many more good years would that buy them?
Any treatment that addresses the aging-associated systematic decline in bodily functions should be extremely desirable. Even if it wouldn't help everyone live longer, it would help a lot of people live better lives nonetheless.
