I don't go by poop in turkeys because it changes so often. I've seen runny and thick, it gets green with more greens as examples. The only time I would use poop as an indicator is if there's blood in it.
Since he seems to be slowly improving, and still eats and drinks I would assume it's an injury of some sort and may take a few weeks, to months to improve enough for him to stand again. Turkeys are big heavy birds that have troubles using their legs after laying down too long. I've seen it in setting hens. They sometimes get up a bit stiff, and need a few moments for the blood to start circulating again.
There are nutritional things like slipped tendons, or perosis, that can be caused by a deficiency. You don't know what he was fed inn his first 3 months. He could of been getting a poor diet, and needs a boost. I think that's why
@R2elk is asking about feeds. Poor nutrition can affect their legs, and lead to lifelong problems.
And are you sure he is a heritage? Broad breasted are notorious for leg problems if kept too long or not fed correctly due to their rapid growth.