Just to clarify: Writing music entirely in the piano roll or on staff paper is a perfectly good way to write music, and it's not "wrong" or "bad" in any way! I just mean to say that using other methods (singing/play along) will lead you down different paths you might not find otherwise.
Of course, if you were actually playing those piano parts in real life, then I have no idea what I'm talking about and you can safely disregard this feedback lol.