While it’s true that there are 2 books is about the labyrinth, there aren’t actually that many chapters depicting his adventure in the labyrinth. It’s mostly filled with miscellaneous things like his training with the paladins, the adventurer guild, audience with the pope, his charity etc. This might be biased, but I don’t think anything is repeated too much as to call it repetitive. All of this miscellaneous things along with the labyrinth adventure is interesting.
Luciel trains almost everyday ever since his contract with adventurer guild, after that there’s the fight with undeads, specter knight sensei and his training with the paladin corps – He’s basically built to fight against human already (Adventurers fights against monsters remember?). But the thing that makes him different with the rest of humanity is [Object X] that he could drink because of his Appraisal and will to live – of which he drinks after each meal undiluted in barrels. Read the effect of [Object X] again (ch5 & ch30), it’s important.
The bosses ARE getting stronger, it’s just that Luciel becomes stronger and fights with better method even if he stays level 1.
– The first boss (ch17) : He killed it without any spell (because it could negate magic). He only uses magic-coated-weapons to kill it.
– The second bosses (ch24) : He used [Purification] and [Area Heal] which is really effective against undead crowds (There are 3 bosses here). He had also trained with the Valkyrie at this point so that he could deal with specter knights.
– The third bosses (ch29) : He obtained anti-undead cheat equipment from the pope. Got more training to fight against crowds with the adventurer guild. Used [Area High Heal]. The bosses them self are pretty much the same type as the 2nd bosses, only with more numbers (5 bosses).
– The fourth boss (ch33) : This is the fight that took him about 6 month. I don’t know how you miss it, but he used [Object X] to pause and heal – while the boss can’t heal himself. Now, let’s say he fights 10 times a day and deals only 20 damage in each battle. In 6 month, that’s a whole cumulative 3600 HP damage. That’s how much of a cheat his method is.
– The fifth and sixth bosses : They’re just to show how OP [Sanctuary Aura] is.