The Air squat is a movement first and an exercise second
In order to squat to full depth with the toes straightforward, an athlete must have adequate ankle and hip mobility and sufficient pelvic/core control. They must also have acceptable coordination and balance. By turning the toes out at an angle, it allows a majority of people to achieve a full depth squat with a more upright chest position. There will always be a few individuals who are simply unable to get into a deep squat position due to abnormal anatomical reasons. Some people are born with genetic abnormalities. With that said, most athletes should be able to reach ass to grass with a squat.
The bodyweight squat sets the movement foundation for other athletic actions such as jumping and landing. Many knee injuries occur when you land with your foot pointing out and with the knee caving in. Players who have to jump and cut will tear their ACL when the knee caves in and rotates.
As soon as you pick up a barbell, the squat now becomes an exercise. For this reason, there are slight changes in the movement pattern that are more “sport specific”. This includes turning the toes out slightly. Doing so creates a mechanical advantage for the squat. Not only does it give us a slightly wider base of support, but it does not challenge our pelvic control and mobility to the fullest extent.
This is why some athletes can squat deeper when they turn their toes out. By externally rotating the hips we can usually achieve a deeper and better-looking squat.
The argument is simple. I believe we should have the capability to perform a bodyweight squat with the toes relatively straightforward. If you cannot, more than likely there are some things you need to work on. I recommend turning your toes out when you squat with a barbell for optimal performance.