MiKTeX and babel: missing file and useless package installation required

The bblopts.cfg from arabi is in tex\latex. You put your version in tex\generic. Now latex doesn't search first the local texmf tree and then the main tree but follows a sort of zig-zag path (see https://tex.stackexchange.com/a/79983/2388).

This means that when the \InputIfFileExists is processed miktex finds first the bblopts.cfg from arabi and so tries to download it.

You can avoid this by putting your local file e.g. in localtexmf\tex\latex\babel.

Side remark: The bblopts.cfg from arabi is imho unnecessary today and should be removed or moved to the doc-folder (where it is in texlive).