Dear Mr./Ms. Bossname,
Congratulations. You win. I resign.
Your efforts to push me out by elevating undeserving, incompetent colleagues while simultaneously keeping my salary static says more about you than it does about me.
I've already secured a new job, and I didn't even bad-mouth you in the interview. They'd already heard all they needed to know about your "leadership skills." Yep, you're Boss of the Year; it's just not the prize you thought it was.
Enjoy running this place without me. I almost wish I could be there to see it.