Have a feeling the mangaka saw an axe in the road and decided to dump the next 4 arcs they had planned and just mash it all into one bigger arc. Just a gut feeling
Ffs, seriously this arc is dragging. We are not invested in this country, only to our FMC, and honestly it's becoming more of an arms length connection. Remember the whole reason was to find her sister and we have already found out that she got BAITED. Our MC is no where to be found and probably...
He also can't go all out because his current body can't handle it. Most likely he would have had better control if his body was up to par, Blew up the mountain cause he's not used to his pudgey body basically.
I hate saying burn the Est Empires capital completely because you know, innocent people and whatnot, but god damnit burn their castle straight to ashes and for good measure destroy any other noble-esque mansions, grain storehouses, and guard barracks as you can cause fuck that country.
Then...