I wouldn't say that his form is fine personally.

Here is an example of Deandre shooting.

Look at where the ball is as he brings it above his head. It's very high, right? Why is that? Well, he doesn't flex his elbows in his shots. You can try this yourself. Try to shoot a basketball as you normally would. Now shoot again, but this time, shorten the "swing" (there's probably a much better term for this) of your elbow. You lose a lot of power, right?

In fact, in a free throw, that's where most people seem to get the chunk of their power from.

Now, his stance is also really weird imo. He flexes his trunk, which I personally like, and I explain this in detail in the first picture of my analysis of PG's shot. So what's the problem? Well, his knees should be fully extended so that all the power gets transmitted upwards. However they aren't as wee see his knees are bent upon release. So he doesn't get as much lift as he could from his knees meaning he gets less power and his release point is lower than it otherwise would be (a higher release point means the ball, which can be modeled as a parabola, needs less power to go in).

We also see his stance means he sometimes stumbles a bit as he's shooting, which obviously will make his shot a little more erratic.

Imo, the first point is by far the most important and that's what I would look to work on if I was DeAndre. Unfortunately, it would also mean that the timing of his shot would be completely different and it would be like trying to add a new mechanic to your shot. In other words, it would take a long time to fix and it would be painfully annoying.