I think Bruce was at his best during the solo days. Not that he has ever been anything but really good. I kinda look at singers like athletes...early in their careers they can succeed on raw talent, but the really good ones with longevity learn proper technique and take care of themseleves to stay great much longer as raw talent (speed, power, voice, whatever naturally declines with age)
I don't see how you can say he hasn't lost range/technical ability. It's clear as day when you compare his power in the higher registers back in the 80's/90's to how he clearly strains and loses the resonance today when he tries to hi the same notes in the same key/register. He's lost a lot of ability in certain areas and that's totally understandable. No singer can do at 60 what they did at 20. You have to evolve. He's done a fantastic job at maintaining 80% of his vocal catalog but I feel he does need to drop some of the high stuff down a half step.