> You should actually 1. run the line starting with echo in your current shell OR copy and paste the line starting with eval into your relevant dotfile.

This isn't right. You should be running both commands in your shell. That's what the brew instructions are saying, albeit in a confusing manner.

The first command makes future shells have brew in their $PATH, the second command applies it for the current shell.

To make things even easier for users, brew could forgo the second command and just ask users to close the current terminal and open a new one. This has the added benefit of confirming the first command.