@Simpleton: What is just up with wizards and being OP in P'n'P-RPGs? By hearsay i know, DSA4.1 (The Dark Eye Ed4.1) suffered a lot under this. Well, having to choose your spells beforehand is a major drawback. I imagined him being more of a DnD3/Pathfinder-sorcerer class magician. Picking very few spells when leveling and choosing them freely in adventure, even if the number of spells are limited to just a few each day. But he a) knows too many and b) seemingly uses too many in a short amount of time. Even the Diablo series limits the number of spells you know, when you are a beginner character. ^^
It's as you said. This is possible, because he is in a "solo adventure". It's an isekai story. But I would like at least a "decent" explanation, why he is so OP. (decent=just nearly anything) There is no cheat skill, no favor of the gods or something at work, that gives him an edge as mage. It looks like every mage in there beginners phase can do that much in that world. Scary. XD
Then again, he does possess a book, that gives him an abundance of information. Maybe he learned all the spells because of it and maybe his Int-state is so high, that he has a very large manapool. I roll with that for the moment.
(Btw, regarding cooldowns: You believe that DnD's spellslots are a strict limit? In DSA5 you have some kind of manapool of around 30-40 mp and most attack spells cost around 8 mp and they deal as much damage as a single weapon attack + some special effect. You can regenerate them by resting. Every 6h of rest restores 1d6 mps. Yepp, you have to roll. Bad resting place reduce the effect. 1d6-1 to 1d6-4. You can sleep 12h a day max. At least you can alternatively chug down a mp-potion. One flask, that lets you regenerate 1d6 mp, does cost as much as the monthly living expenses of 1 person living an acceptable/neat lifestyle or a family for 4 in the slums. It drives you into bankruptcy, but hey. Imagine going *pew*, *pew*, *pew*, *pew* and then being dead weight for your party for the rest of the adventure. XD Yepp, magicians got nerved hard from DSA4.1 -> 5. A step into the right direction to tune down the damage potential of magic that some other RPGs should follow. (But maybe with a bit more regeneration. That DSA5 example is really a bit too harsh.))