If X is built on top of Y, and I should generally be using X, then the docs for Y should absolutely say that. Burying that away in some hard-to-find tutorial is not good practice. We could argue for a while over the exact semantic meaning of 'deprecate' and whether Y is truly deprecated if 99% of the time when you use it you should really be using X instead. But I'd hope that we can both agree on the central point of my argument here, which is that in Unity it's often incredibly difficult to figure out which of 5 vaguely-similar-looking APIs you should be using, and it's a bad sign when the best source of info is a "coming soon!" message on an out-of-date tutorial not even linked from the documentation.

Perhaps you should explain how I've misunderstood GetComponent.