So. I'll provide some advice that has served me well in the legal field (which is highly contentious).
When I was a baby lawyer, my mentor recommended that, when I get mad and want to tell somebody off, I write the letter I want to write. Say everything you want to say. Hold nothing back. Then print--but don't send--the letter (or email) and put it in your desk drawer for at least 24 hours. (48 hours is better.) Then take the letter/email out. If you still feel the same way, then send it as is.
In 23 years of practice, I have never sent that letter as is.
Your message says that you want to "leave on a high note and with grace" but you do not want an "it's time for me to move on and I wish you the best of luck message." I submit those two desires may be in tension with each other -- leaving with grace probably means wishing them the best of luck, holding back the things you really want to say, and instead saying those things to a trusted friend or confidante who won't mind your ranting to them. (My wife serves this role for me.)
Just my two cents. I suspect your local musical community is pretty small no matter the size of your town/city, so leaving on a high note and with class will serve you well.