I don't believe FL sizing will correct thinning in the body..
For one, shoulder bumping doesn't shorten anything below the shoulder.
And second, sizing the body inward will not thicken the wall where it has stretched, anymore than elsewhere(so it's still the weak link).
I think it's a good idea to monitor it if your loosing brass(trimming). That brass came from somewhere, which came from somewhere, yadda, yadda.
I also think the only ways to address it, is to toss after so many firings, or prevent it to begin with.
There is a misconception that FL dies take everything back to a 'standard'. This is not true at all.
FL dies, like any other, simply squeeze brass where there is an interference fit.
There are so many things that affect that fit and take...