How Doctor Who Ruined Davros...well kinda

Davros is a character first introduced in the brilliantly acclaimed episode Genesis of the Daleks with Tom Bakers 4th doctor. He is the creator of the Daleks. Seen in his life support chair, with facial issues & a big blue eye to accompany it. The character has only appeared twice in NuWho with David Tennants 10th doctor & the 12th Doctor Peter Capaldi. But how did doctor who ruin the character?