There is absolutely no one size fits all squat position. If you don't believe me, you are in for a treat. This article will help show you why athlete comfort should dictate squat width, why people's feet point out (no matter how much "mobility" work they do), why some people have a really hard time squatting deep, and why some people are amazing at pistols while others can't do them at all.
The hip joint is basically made up of a "socket" on the pelvis (called the acetabulum) and a "ball" at the top of your thigh bone (femur), which we call the femoral head. Around the hip joint are a lot of muscles, a joint capsule, and connective tissue. There are many other anatomical considerations when considering a squat, but let's focus on the hip.
When someone has difficulty squatting, or their feet turn out, or they like a wide stance, we all want to jump on the hip mobility bandwagon and say "your hips are tight bro, you need to mobilize them". If we say that without considering anatomical variations of the hip joint, we can be seriously misled.
Let's take a look at this first picture. Here we have two femurs from two different people. One points more upwards, the other points more downwards. Do you think these people will squat the same when they have that much bony difference?
Athlete's won't squat the same, and they SHOULDN'T! I hope I shed some light on the WHY. Athlete comfort will dictate the stance that puts their hip in a better bony position. There are narrow squatters and there are wide squatters. That may have nothing to do with tight muscles or "tight" joint capsules and have EVERYTHING to do with bony hip anatomy.
Very few people are at the end range of their hip motion, so hip mobility drills are definitely a good idea.
People will express their hip mobility in different planes, and that is not a bad thing.