the fear of missing out a better compression

I prefer .tar.rar.tar.

Zip, RAR, 7z etc. store and compress the files. Tarballs work differently, tar stores the files and the second program compresses the tar as a continuous stream.

They originated in different mediums, programs like zip were born to deal with folder structures, tar was created to deal with linear tape archives (hence the name).

Kind of redundant. Both .zip and .rar store an index of files within the archive and are a bit 'inside-out' when it comes what we get from tar.gz.

That is, ZIP is pretty close to what you'd get if you first gzipped all your files and then put them into a .tar.

RAR does a little more (if I remember correctly), such as generating a dictionary of common redundancies between files and then uses that knowledge to compress the files individually, but better. Something akin to a .tar file is still the result though.