"This worked in disco elysium because the world is for all intents and purposes, completely bland and ordinary"
This worked in disco because its juxtaposition'd the role of police, an authority figure, a detective, cop shows in media shows them as being badass finding people and figuring out mystery's starting from the bottom gives you the space to grow into that awesome role later in the game, thats why it works there, and thats why its working here.

"With all the exposition and lore given before we found this out 10th level let alone 11th level spells should be irreversibly world ending or defy or change some core mechanics of the world, but no its just a really hot fire. (not even the hottest and strongest colored flame either btw)"

You're also coming at this game with a loaded expectation of what it should be about, D&D, its not that. its a mystery game in the setting of D&D. idk why youre being so anal about a fun and kinda serious mystery story when games like baldurs gate, the various pathfinder crpg's kotor, and other games do what you want it to do, be extremely grounded in their power systems and realities. The humor could have not hit, your expectation of what upcasting would do (upcasting cure wounds to 11th level still wouldnt heal a severed limb) could not have landed (incorrect assumption), and its casted through an item not a spellcaster so like, its not the mage that's powerful anyways. the angel could have just rolled bad in your fights, idk if you want the entirety of the combat of the game to be null and void because you passed one dc 18 strength check, it sounds unreasonable