Arean's back lever is not perfect yet, but he came a long way, from when he started!
It's a movement that is harder than it looks.
Not only because of the strength component but also the mobility requirements, because the bar is behind you.
This alters our perception and body mechanics (similar to a handstand, or just standing on leg with your eyes closed, for example).
That means the back lever requires extra focus on legs, hips, ribs and shoulder placement.
Here is how to practice the back lever with negatives, IF you can already do a good static tuck hold: