I'm confused about the question and I'm even more confused about the first answer!
So, here's another question. What the difference between 'Journal' and 'Pages', 'Reminders', or any other inbuilt apps that can be literally used for typing things out? These other apps can't/won't dynamically prompt you to type out something based on your life and what you do in it, or other more generic prompts.
Yes, you can use Notes to type out what you feel, keep doing it if it makes you happy and works for you. My first journal entry last night prompted me with my walking workout and a picture of kittens I took at the adoption shelter at the mall. It felt nice to talk about how it made me feel. Looking at the app right now, it is showing me recommendations for talking about special people in my life, specific sets of photos from past trips, and have any of my beliefs changed recently.
Yes. I'll agree Journal is a little rough around the edges right now; only basic filtering and no search or export. Will Apple change those? Maybe, Probably, Maybe-not. Will I use this app everyday, probably not, I'm not really the "journaling" type, that's ok too.
As for privacy, Apple is showing end to end encryption, and uses on-device processing for the recommendations. If you don't trust Apple's privacy policy regarding this particular app, why would you continue to use Apple products at all for the same "privacy" reasons?