I found the title of that section slightly triggering too, but the argument they lay down actually makes sense. Consistency helps you to achieve correctness in large codebases, because it means you don’t have to reinvent what is correct over and over in separate pockets of the codebase. Such pockets also make incremental improvements to the codebase harder and harder, so they do come back to bite you.
Your example of vendors doesn’t relate to that, because you don’t control your vendor’s code. But you do control your organisation’s.
Nothing wrong with them! But since I want to build another tool on top of it (for fiction/novel outlining and writing) I figured this was a good exercise to become familiar with the codebase. And since I still do some Rust development, having control over both my IDE and my writing software seemed an added benefit :)