I agree 100 percent!
Arthur fleck is the black and white television. The joker that rivals Batman is the colored upgrade. A man of intelligence and guerilla warfare capabilities.
Everything has an evolution or improvement process. Arthur fleck is too lacking in number of skills that can come close to rivaling Batman. That and he is way too old to be batmans rival.
By the time Bruce Wayne is in his late teen, Arthur is going to be an old man. I would imagine that he is going to be a mentor for the real joker. Him sparing that little dude shows that he is capable of being kind to someone he sees as innocent.