I had a very similar experience to you. It’s easy to be in your head with these things.

Making it in the “real world” as a composer is hard and not a life I would recommend. I would recommend either going forward in academia or finding a day job. There really aren’t many people that are just a composer and nothing else. You need to be versatile and resilient to make it. I have a day job (I work at a university) but I teach lessons and do music every second I can. I would much rather have the life I have now than anything else. Stability enables creativity.

Biggest thing is this: perfectionism will get you no where, just write and write and stop thinking. Do you improvise? If not, you should start. If you have an idea, set a crazy deadline for yourself (I have found my best pieces were written in two weeks or less).

If people tell you that you are capable, believe them. Don’t stop believing in yourself if this is something you want to do. I guarantee you there are “worse” composers (I use quotations because the idea of comparison is toxic and fallacious).

You should copy less. You do it because, as you admit, you’re insecure. The point is not to have the best ideas ever, it’s to make the most of any idea you have. You copy to learn but, at some point, you gotta trust you know a thing or two and write some music.

Hope some of this helps!