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. 

With the exception of Beerus, there is no precedent. And doing it in desperation make sense, but if he shot the planet and it took 4 minutes to blow up, they would be screwed because Whis can only go back in time for 3 minutes. 

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.

They said that and I understood that, but what about the more casual watchers, but it was literally, Frieza winning then Goku winning it wasn't gradual at all.

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

I didn't even care about the 4 months of training because he is Frieza, a mutant, who basically took over the galaxy without even training, and you need a body to train in the afterlife, which you cannot get in Hell and rarely get otherwise, which is why Vegeta became weaker in the Buu saga.

Super Saiyan Trunks wrecked all of Frieza's soldiers in like 2 minutes in the Android Saga, now we spend half the movie fighting them