However, the package does work as expected and the final file size is as expected as well.
As Fellippe said, it works, and that counts...
For everybody who needs to save some disk space, you may safely delete the folowing folders from the new MinGW package.
internal\c\c_compiler\licenses,
internal\c\c_compiler\opt,
internal\c\c_compiler\share
Although these folders must be present in the distribution (license requirement), you don't need to keep them on your private PC, as it's mainly explaining text files, lots of Python stuff and optional packages, which are not required for compilation of our QB64 programs.
Deleting these 3 folders on my PC did eliminate about 2/3 of all files in the MinGW package and freed up 113MB disk space.