About the plot the author found a intelligent way to justify people reincarnating in this world and becoming adventurers: since most people of this world won't risk their lives exploring those countless dungeons, we might as well recruit dead people from other worlds and force them to be adventurers.
This also could serve as excuse an to introduce other OP parties later on: people who, like the MC got reincarnated were forced to become adventurers and were lucky enough to get a OP job.
But if this information about otherworlders being forced to be adventurers leaks I could see chaos happening, since at this point there must be a lot of otherworlders living in this country.