Definitely isn't the latter. Numerical Recipes and Hacker's Delight have tons of gems that you won't get from an LLM, or that an LLM will even understand despite appearing all their training sets.

Even before LLMs became big I started hording solid technical books, as there was so much misinformation on Google/SO that any non-trivial technical question could not be answer without a high probability that the answer was fundamentally wrong.

LLMs are super helpful for learning, but without the foundation of a true textbook at your side they will very easily go off the rails into a world of imagination.