You arent adressing that he is a tanky mobile flanker that dominates the game when unnerfed, and such an issue isnt solvable by just nerfing rocket punch and buffing everything else.
The reason why Blizz keeps buffing RP and nerfing the rest is because RT has clear counterplay and weakness windows. When you center DF around the rest of his kit, he becomes this 250+ hp tanky flanker with CC and an annoying escape tool that doubles as team wiper when comboed.
DF has identity issues AND suffers from a lack of real mobility counters in this game that isnt just CC+burst.
I really want DF to be viable, but I can understand why Blizz keeps him half broken and half too nerfed.