> These bones are much larger than what the dragon would theoretically need to support their own weight, even when landing.

Life is a fine balance between different needs, and as such it hates whatever is "much larger than needed", because it's a waste of resources which could be better used for something else. That's why unused muscles shrinks and used ones grows. 

If your dragons are putting their resources in growing bones larger than needed, they will be underdeveloping other organs or functions, with the result of becoming unfit for their environment.

One possibility would be that their daily calcium need is lo large that, in order to keep their bones healthy, they spend most of the day gulping stones instead of hoarding gold or trapping princesses.