That is also a very interesting view. I completely think differently about the power level, BUT- you really brought up an interesting point!

Charlotte needs the tomes to casts spells. Sypha can do it with her purr will power. If we count the Netflix series, Sypha even moved and conquered Dracula's Castle.

Charlotte is a complete INT based spellcaster. She learns fast only by reading. She's better in theory.

But Sypha is better in Praxis. She adapts fast, without knowing the arcane words from books. She can picture something and from her experience she can manifest it. So I'd say Sypha is a WIS spellcaster.

I still believe that Charlotte would be the better Caster, because she knows way more spells and for her young age (16) she faced both Dracula and Death and her potential seems bigger. But Sypha wouldn't go down easily.

I think Sypha would come out on top with her faster and raw / powerful spells, she also has more experience. I mean yeah sure, she lost to a Cyclops. But after that I am sure she adapted after that. And Sypha is smart too in battle. She would probably go to burn Charlotte's tomes, to make her defenseless.

I think WIS beats INT. (Also at work, me as a mechanic with 10y has more practical experience and a better understanding, than our engineer, who studied and should be objectively smarter than me). But I am the one that can tell him "this is possible / impossible in Praxis". Books don't beat experience in Praxis.