Not underestimating his strength at all. You are kidding yourself if you think he can carry an object that gains mass as it extends, especially since the further away the weight of something is the harder it will be to hold. Definitely not like the hulk, even Hiruzen's knowledge can't transcend Universes.You're underestimating hiruzen's strength, man. The guy is like the hulk, didn't you see the 6 packs?
Also I would like to say this. Itachi is also above Hiruzen in planet busting status by your logic. Totsuka can seal anything. Enma is something, if enma's mass tends towards infinity then so does his energy. Totsuka therefore can seal infinite amounts of energy that can planet bust and stop hiruzen from planet busting. Since he can seal something capable of planet busting with totsuka, totsuka therefore has the ability to seal the planet. All while stopping hiruzen from planet busting. Itachi> All forms of Hirzuen. GG.