Did you see the movie? The blast was moving at a snails pace at first and Goku could have dodged it trivially if it weren't for the fact the Earth was behind him. The observing Z fighters outright state that the blast will destroy the Earth if Goku can't stop it.

Spoiler: Back to the 1st Episode
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Remember after Revival of F how so many people complained about Gohan not learning his lesson when Majin Buu showed up after Cell proving that slacking off his training was a terrible idea? Judging from Piccolo's expression as he observes Gohan that's going to be a plot point in Super.