Okay, I assumed the world he transferred into as the >origin< world of the skill. So if he would have transferred into another world, he'd get another skill with the same name and effect, but designated with another level, correlating to that worlds difficulty. If the origin world, which is meant, is Earth though, that isn't easy to see. Maybe it is that high, because Earth is a world without magic to protect/heal yourself, there is the threat of a nuclear holocaust and global warming is a thing. But then again, there are no magical deathrays or mind control, no dragons/demons/liches and global warming comes with the cozy blanket of enough to eat (when not disturbed) and modern tech.