He only appears “shallow” because George Lucas didn’t really give him much to do in The Phantom Menace.
You’re literally confirming that he’s shallow with that statement.
Maul was featured prominently in TCW and Rebels, so TPM is not the be-all, end-all for the character’s development.
It is in my world, and many many other people who just watch the movies feel the same.
And therefore he was last seen getting cut in half.
And therefore his appearance in this movie is not just dumb, it’s nonsensical.