after thinking about this I realized that the first RainBoom is an outlier for rainbow dash, she has done the rainboom plenty of times and never has it done anything like what the first one did. maybe outlier is the wrong word but adult Rainbow Dash has never managed to use the Rainboom in such a way as the original nor has she shown such endurance after it such as when she broke her wing from a simple crash and got knocked out for an unknown period of time in read it and weep
Rainbow making a ‘Mushroom cloud’
stirring up all the dust in a dusty old barn that she was trying to take down so applejack can make a new one doesn't count as a Mushroom cloud, seriously by definition there would need to be radiation in the cloud for it to be a Mushroom cloud i'm sorry if I come off as rude but i'm sick of people calling anything in that shape a mushroom cloud.
Moving the sun and moon
my opinion is how we are currently handling it.
Luna hitting the moon
I believe it shouldn't be used because it implies Luna physically hit the moon when most fans agree luna was sealed inside of it do to its appearance changing after her banishment
The First Rainboom being Heard across EQuestria
it was not across the country where did people even get that? we see it form the main 6 perspective they were all around ponyville I will account for all of them below
twilight, we can see the curves spreading to the sides in canterlot were twi was so the explosion started not far from canterlot and you can see canterlot from ponyville so it can't be more than 3 or 4 miles away (rough estimate)
rarity wasn't far from ponyville I Know she says she was very far away but she's a drama queen and probably exaggerated I imagine she would have only needed to go a mile to say that after all she got back there the next day and had redesigned the outfits and didn't seem tired at all
the only one we don't have any kind of way to measure is pinkey who was at the rock farm but we can assume its some what close to ponyville considering the next one
Applejack could see the burn at sweet apple acres from where she was in the city and suw no signs of the boom meaning she must have been the furthest away of any of them sense sweet apple is meant to be nearby ponyville but on the outskirts so this makes sense she would be the farthest away of the main 6 from the start of the boom
both Rainbow and fluttershy were by the start of the rainboom
we can't use the map to scale EQuestria size it would be 100 miles wide MAX,sense you can see canterlot from Ponyville and there's a notable distance away it's probably not to scale and is most likely only set up so all noticeable locations can be seen and represented on the map so the main 6 know where to go, just look at the Map
either A it has the most diverse landscape ever after or,
B The map isn't to scale and EQuestria is really big.
even if we assume the distance is something like 10 miles,(huge high ball in my mind) there is still no way the distance would be over 200 Miles. Thats too small for what is supposed to be a huge Country there are some US states that big. (Alaska and California) so the map is likely just meant to basically represents EQuestria and not be an exact scale model of it.
pinkey 4th wall
I really don't known how to handle that other than the events should scale to no one