The were RIRs and EEs and they couldn't jump up but a foot or so, and they struggled to walk fast. They were only 5 years old.
Five years is fairly old for most chickens. Yes, they can live to be older, but many don't.
As for the rest of the symptoms, they may have been obese, or they may just have been out of shape from having little to no exercise.
Which food the person was feeding would also make a difference. Layer feed (pellets or crumbles) is meant to be available free choice to hens. But if the person was feeding something like corn or scratch, it would not provide all the nutrients the chickens need, so they would be expected to have problems.
Also, when developing a feed for the chickens to eat as much as they want, the companies are really only trying to make it work for 2 years or so, because of when commercial layers get butchered. So it might not be quite right if they live on it for 5 years.
So I don't have a good answer to your point, but I still think that most flocks of laying hens will do better with unlimited layer feed, rather than limited layer feed and expecting them to make up the difference from a semi-random collection of other stuff.
