Tobirama stronger than Hiruzen, Minato, Kakashi Hokage. Hiruzen will be helpless against the flying god of thunder despite being able to wield all 5 elements. Kakashi without sharingan is also powerless. And Minato can teleport and attack while Tobirama can do both at the same time, plus Minato needs to use kunai to teleport while Tobirama doesn't
Madara is the person who rarely praises anyone but here he is actually acknowledging Tobirama. He calls him the fastest shinobi of their time and even points out how lucky he is that Tobirama can't use his full power. On top of that, he says he is the one the heavens are smiling upon implying that if he was at full power, Tobirama might be the greater threat.
