Finally an Isekai power I can get behind, the ability to separate your meat from your skeleton and have both be fully functional, like a ghetto Noob Saibot.
He's both a high rank Necromancer and a high rank Healer. Since the dark and light magics are diametrically opposed to one another, the crystal ball couldn't detect either because they canceled each other out. To all observers, he's a magicless wimp. Except he's very much not.
The summary also implies
Despite being OP, he's left working at a warehouse doing day labor instead of adventuring, because the princess tricked him into walking through a death forest into another country, so he's officially not her problem now.
Dude NGL the manga kinda is meh based on the LN, but the scan group seems pretty sick. You gotta get a better quality/proofreader to fix up some glaring TL mistakes, but the TL is literally 100% or 0% so just gotta manually fix the 0% situations. Since it's AI it'll learn more effectively when corrected (I assume) so it'll eventually get better.