The kung fu pose you are showing, and the yoga poses I’m speaking of are different things, do you get that?
Yoga has the kung fu like horse stance, whatever you want to call it.
Yoga also has wide stanced poses. There are right and wrong ways to do them. The primary strain is on the knee joint if you do them wrong.
I would know, I did yoga several days a week with a hard-corp yoga/dance instructor when I lived in NOLA , for seven years.
The human skeleton supports the weight of the body. It’s articulated at the various joints. It’s an endoskeleton, as opposed to an exoskeleton (crustaceans/insect, for example).
The muscles contract and relax to move the skeleton and and hold it in whatever position (let’s say upright, normally). The connective tissue connect muscle to bone (tendons), bone to bone (ligaments), and muscle to muscle (fascia).
Muscles can provide stability to joints (like, when I tore my ACL, I did a lot of squats, and hamstring curls, and calf work to protect my knee joint. It works to some degree. ). Once I quit lifting, I rode my bike a LOT for the same reason.
McGregor’s calf development, lack thereof, or his “oversized” upper body, I do not think had anything to do with the leg break he suffered.
I can’t rule out other factors as you mentioned related to his drink/drug/training habit. But you can’t rule them in either.
Connor has been training for years doing weight bearing exercises. This tends to make the bones denser and thus stronger. Including his fib/tib, which bear that weight with the rest of his skeleton.