Even when you feel that what you write "lacks of substance", you should finish it, read it again and start editing what you feel you need to change. That's what I do. I start writing and then creativity hits when I read it again. Try it, you'll see it works.
About the ecchi thing, I felt the same way when watching Highschool DXD and I dropped it, but in that case I didn't find anything else worthy to keep watching it. It was different with Fire Force, because this story is intriguing and make me wonder what happens next, that's why I kept watching and decided to re-watch from the beginning.
Thank you for reading my review, I really appreciate it.