Mmmh...the manga changed some parts that were important, like the princess using a light brainwash speel at the class at arrival so that they would accept the mission without asking questions and the MC being immune for hisown barrier, plus the childhood friend having some barriers too because he protected her as second nature.
They even skipped on the kingdom checking their potential and the MC as usual faking his status.
MC was sent back from the kingdom when his mission was completed but something gone wrong and he was killed and reborn in the modern world where he decided to check every possible way to return, that is why he was not interested in the moder world society and never stood up for himself, that made him able to recognizeisekai cliche but wasted away his school life, a little dumb.
The crossing of time between the world was different and in the isekai just a few years passed.
He could trash the kingdom with ease but decided not to because after that his classmates would suffer and he doesn't wish to carry them, he doesn't want them to die to his actions nor help them too much, for that reason he didn't block/dispel the princess magic.