Interesting how easily you make loud claims having no context...
Have you ever thought why people make mistakes? ;)) Mistakes are not related to knowledge in general and understanding in particular. Otherwise, you would never fail with tongue twisters based on well-known words with a clear meaning, no matter how complicated they are.
Don't take this the wrong way. Nice write up. :)
......
Sudo ... why would you sudo a command that you don't understand?
RTFM ... all of the behaviour you experienced is well documented. There are no surprises.
POSIX and UNIX utils are flexible and powerful. This is why we love them. Don't blame the hammer.
Sandbox anything you extract and review it. Extract in a test environment. Extract without sudo and copy the files and permissions you need.
tar -tv is simply tests the archive and outputs the paths. You ignored what it told you - that it would overwrite ./ :)
#### Never ever do this! $ sudo tar -C / -xvfp xbps-static-latest.x86_64-musl.tar.xz
Insanity.
Cheers :)