I don't know how much of it is the singer's fault... the whole song could use a lot of work.. the guitar parts don't really match anything... so of course it's gonna be hard for the singer to do anything.. he's not the greatest screamer, but there is more to music than how it sounds.. writing music is important too... instead of just replacing him.. tell him what sounds like crap, and what sounds good.. then he will evolve into your ideal singer... similar situation happened with my drummer.. he would do weird fills, we told him they sounded like crap, he stopped, and now he's a good drummer