uhm, yes it is with init, since in case you use the composer symlink it makes sense to call vendor/bin/RMT init, otherwise the command.php would needed to be linked there.

and then frankly, i'm not sure why running it from outside the project root is such a big deal to you. running in your current environment is kind of consistent behaviour.
Most shell tools don't have a behaviour where they favour some guessed setup over the current runtime environment. (have you ever run ls and expected it to give you the contents of a different directory, without you naming that dir? have you ever noticed where unzip puts stuff if you don't tell it where to put it? phpunit? phpcs? 

Adding an information to the docs is never a bad idea.