People might not know what the code base is actually like; they have incentives to overstate its quality; and, even if they can point you to a relevant, authoritative book, that doesn't entail that the hour spent with it is better than an hour spent learning a tool.
I still disagree, but I think I better understand the disagreement now. I find it easiest to learn a new language by starting with the canonical beginner's book, e.g. the Pickaxe book for Ruby. I find it hard to learn tooling like CI/CD, logging/metrics, etc by reading or through personal projects, I much prefer to learn those on-the-job as necessary. It seems like it might be the inverse for you.
Even if a new codebase isn't exactly 'Effective Java' quality, it's good to have that reference to better articulate to yourself exactly how the codebase is flawed.
People might not know what the code base is actually like; they have incentives to overstate its quality; and, even if they can point you to a relevant, authoritative book, that doesn't entail that the hour spent with it is better than an hour spent learning a tool.