I've read the Secret Wars recently...Hulk is by no means an intellectual during the Secret Wars. He's no neanderthal but he is using short unintelligent sentences.
Titania and a couple of other baddies started their assault on the good guys, who were fleeing from Captain America's recently destroyed base. Hulk was like carrying 4 super heroes, and when the good guys ran away, the bad guys started hurling huge pieces of Captain America's base of operations at the good guys. Iron man blasts one piece that was thrown into several thousand pieces helping to protect the already fatigued good guys.
Then Owen (molecule man) lifts up this mountain range and drops it on them. I think the reason why the impact of the mountain being dropped on the planet didn't destroy it because 1. hulk caught it 2. Beyonder built the planet out of several different pieces of other planets and pieces them together using his awesome power. I think that power held the planet together regardless of what damage it took. Even blasts from Galacticus.