How Doctor Who Ruined The Master

The Master alongside the cybermen and daleks is one of Doctor Who's Most iconic villains. Played originally by Roger Delgado who appeared alongside the 3rd doctor back in the 70s, the master became an iconic hit going against several doctors including the 4th doctor and even the 8th doctor in the TV movie. When doctor who was rebooted in 2005 the master appeared played by Derek Jacobi alongside David tennants 10th Doctor before regenerating into John simms iconic master who ruled the world twice and made the doctor old. He was defeated when this master the Saxon master, was shoot by Lucy Saxon his companion and life partner. He refused to regenerate and was later bought back in the 10th doctors regen story with an emphasis on the timelords and the masters insanity with the sound in his head. He would later reappear as Missy and go on a character redemption alongside the 12th Doctor Peter capaldi. Missy would battle on being good before the Saxon master would return and turn the doctors companion at the time, Bill Potts into a mondassian cybermen. Missy would turn good and kill the Saxon Master and to stop Missy joining the doctor he lazar screwdrivered her. She would later die. The master would return in jodie whittakers run going from good to bad and ignoring the previous character development. What happened? Why was the ignored? and by this point like the cybermen and daleks had the master become overused and has this ruined the master?