What it says on the tin, If Diaz had been the Leader of Italian Forces since the start of the war, how might they have fared?
Well, being worse of Cadorna is very difficult and unlike the OTL commander in chief, Diaz had fought and has not always been an armchair general.
While not a strategic genius, Diaz know that treat the men like shit and eliminate everyone that even think differently by you...or can be used as a scapegoat for your failure is not a great incentive for cohesion and morale, plus Diaz just for his personality will have a better relationships with the goverment as Cadorna, as a true follower of the 'lonely man at the command' theory demanded basically dictatorial power to wage the war.
While this will not magically create a breakthrough of the austrian line, in the long run we will have an italian army with less casualities, an officer corps more capable and with more autonomy and if/when the Caporetto Offensive will come, the possibilty of an a total collapse of the front will be severerly decreased
