AI can give you 1000s of exercises and explain in great detail exactly how to solve them, and what you're doing wrong, as well as where you suck, explore other ways of solving and where you should improve. Learning to integrate or solve differential equations with Gemini is 10x better than even the good teachers I've had. It beats bad teachers because it's just simply better than them, and it really increases what you can learn from good teachers.
And the same goes for critiquing writing, whether code or prose. I do prose like 1/10th of the time, code much more often, but the problem with my writing is usually relatively basic grammar and consistent style problems. Also using codex with "I've written X, break my code" usually gives ... I should say usually more insight than I was ready for.