I don't think I'm a better writer because I have always kept a journal. I think I'm a better person. Journaling is about self reflection. It's therapeutic. It helps you learn how to sort your thoughts and better understand yourself - all things that can improve your writing. Honestly after reading this I feel like you would benefit immensely from it - especially considering your perspective that non-paid writing is a waste of time. Do athletes think their time in the gym is a waste because there's no audience or competition to win? No, they do not. At least, the good ones know that unpaid, unacknowledged practice is never a waste of time.