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I don't get your problem with Earth's destruction. Freeza did destroy Vegeta (the planet) with like 1/100 of his true form power, and held back too much at Namek. After his power up, it's not unreasonable that even on his weakened state he could destroy a planet in the swift fashion Beerus does.
Not to mention stamina drain from super-strong forms has been around for ages, Freeza lost the first time doing the same thing, same with SS3 Goku against Majin Buu. Same with anyone who tried to fight the infinite power supply androids (18 and 17) before ascendend SS.
My only gripe with the plot of the movie is Freeza going like "four months of training should suffice". Unless he trained close to a black hole, or another time room, that was a fairly crap explanation for his power-up. They could even mention he trained all that time in hell, but no, apparently all you need is four months of training... :D
