So if i understand correctly, spell lvl arent divided to class Progression but rather spellslot progression of the highest class whilst unlocking via multiclassing? Very interesting.
With the caveat that this is just my inference from what Larian have said in interviews about multiclassing, and my EA observations of how the game handles this stuff and what would be easiest to implement.
But I could be completely wrong. It wouldn't be the first time!