When I played trpt going through grade school, middle school, and high school (in the 60s and 70s)I took lessons. Also in college on trpt and sax. I think alot of kids don't understand that a teacher is a long term helper and not just someone to take a lesson or so and then off on your own. I think the greatest value of a teacher is that the student literally doesn't know what they don't know. In other words as a student I didn't know that I needed to work on time (try playing with anybody without it) , intonation (note sounds weird, whats up?) and I had no idea of a progression of books and exercises that would take me in a direction of improvemet and maturity. I did know that the first chair and better players all took lessons.
I think things have changed a great deal currently, with the music programs of alot of schools being underfunded or cut. Also, it was my experience that over half the kids in school took lessons so the overall band was better just walking in the door before the director got there. So, my point. If you really would like to get better at playing and want to see consistent progress (even if you don't understand what that progress sounds like , and that is a constant theme with students going it alone) get a teacher and stick with it for 6 months or so. The benefit is easy much, much, more that that shiny "good" horn that you think will change your playing. Good luck. K