No, I don't think Djokovic has "declined" that much either, and Federer also was great much longer than some people say. Of course his body gave up NOW, but in 2017 he PLAYED close to his best. Again, played, not moved. But he partly compensated it with improvements due to the new racquet.
And you are right, on clay 2019 was not the best year, but on hardcourt it was. As I said, he was much more prone to upsets in his earlier years. If he would play for my life, I wouldn't have trusted him off-clay in the years some people call his "prime", but I would rather trust him now. On clay I would take the 2017 version. Moya contributed massively to his game.