You're right that nobody became brilliant through spaced repetition. But spaced repetition is not meant for that.

Spaced repetition is not meant for conceptual things or skills. It's meant for only the simplest of facts.

It's meant particularly for foreign language vocab, names and quantities in medical school, names of cases in law school, that sort of thing.

It has little to no relevance in math, physics, and engineering.

Just because it's not meant for all things doesn't mean it doesn't excel at some things.