I haven't read Dungeon Crawler Carl yet, but that should fit your criteria right? Many of the progression fantasy books usually have a magic system with tangible tiers and usually rules are known too.

Cradle by Will Wight and Mage Errant by John Bierce are both complete series and I'd put their magic system as hard. Mage Errant dives deeper into the workings, especially as the main characters are students and one of their teachers is especially knowledgeable. Arcane Ascension by Andrew Rowe is another series with such academy focus and a progression magic system.