When I give an analogy of a players shot, my typical go-to is a catapult. Your lower body is the base of the catapult, and your shooting hand is the arm of the catapult. The beautiful part of the catapult is that there are very few variables. Theoretically, you get it aligned, then figure out how far back to pull the arm and fire away. Want to keep hitting the same stationary target, all you have to do it keep puling the arm back the same amount. (I’m oversimplifying a little to make a point)
For some reason your catapult moves between “shots”, and on the second shot it is now leaning to the left, then the boulder is going to miss left. You need the base level to fire straight.
The same thing happens in the base of our shot. If you push unevenly with your legs, your upper body will lean one direction, and you will either miss that direction, or need to create another “mistake” in the opposite direction to cancel it out. Either way, your habits are getting complicated.
On every shot we should be trying to push as evenly as we can with out legs. Push evenly with both legs - your centre of gravity moves straight up in the air and all you have to do is follow through straight. Push more with your right leg - you lean left, you need to follow through (or something else) right to compensate.
Of course, we are going to make mistakes with this. Not every shot will be perfect, but we should be trying to build as perfect habits as possible.
To help your legs push evenly, put them in similar positions. By this I mean, avoid a large stagger in your feet. If you have a large stagger, your legs are in dramatically different positions and will do different things. This makes it harder to push your centre of gravity straight up in the air. But get your legs in similar positions and they have a better chance.
In a perfect world, I would want feet totally level when you shoot. No stagger at all. But shooting a basketball isn’t a perfect world. In reality, as long as a player or coach can look down at the their legs and see that they are in a very similar position, we are in good shape.
In these types of situations, remember the letter of the law, but also the spirit of the law. The letter of the law would say “put your legs in EXACTLY the same position”. The spirit of the law would say “basketball is challenging and you don’t have time to be perfect all the time, but try to build as perfect habits as possible”.