Your post makes me realize that we actually need more information. Is that 6-run drop from 32-34 around the amplitude we might reasonably expect to see in the career of a given player, or is it a statistical artifact of the fact that more players are declining than improving? If player A drops by 24 batting runs between 32-33, but players B, C, D, and E stay flat, that would produce the same average as if they lost 4, 5, 6, 7, and 8 runs. (Check my math.)Looking at that aging curve, though, Hanley's decline from age 32 to 33 is already an outlier in its severity (about 26 batting runs according to FG; I don't want to bring defense into it because of the apples/oranges issues raised by the 1B-to-DH move). He was only supposed to have declined about 2-3 runs this year. If he actually follows the aggregate trend from age 32 to 34 (about a 6-run drop), that will mean a substantial improvement next year, and a performance that's much closer to his 2016 than his 2017.
In other words, projecting him to be much better next year doesn't require us to assume he's a freak of nature.
I guess I would want to know how many players gradually decline versus completely implode before I try to apply these curves to individual cases.
But I don't think this gets Kielty off the hook.