I wouldn't say he ruined him - he just gave us another take on him. The Batman of the '50's is completely different from the Batman of today, yet they're both the same character - the same is true here. Denny's Vic Sage is the same one that Ditko created, he's just had a change of attitude - and let's face it, Ditko's Sage is a mean son of a bitch, designed primarily to provide an outlet for his creator's political views. That's fine for single-issue stories, when the point is basically to provide a quick hit of action and adventure and then leave, but it'd be a little difficult to pull off an extended story arc with a character like that - he's just not very relatable. He needed a change in order to transition into the modern world - and I think O'Neil did that very successfully.