Does the 3 backup contain any 3rd party addons or theme setting not present in your 4? or non-compat with 4?
Don't run Windows myself, but ... might try the following ...
In 4.0.highest there is a restore_backup.php script in code/admin/cli/.
Help on that script shows:
Restore backup into provided category.
Options:
-f, --file=STRING Path to the backup file.
-c, --categoryid=INT ID of the category to restore too.
-s, --showdebugging Show developer level debugging information
-h, --help Print out this help.
$sudo -u www-data /usr/bin/php admin/cli/restore_backup.php /path/to/backup/file.mbz --categoryid=1
Since you are on Windows, no sudo in front would be needed and you would have to change / to \ with Windows stuff, but note the -s option shows debugging and this is just php talking to your DB then ... web service out
of the loop.
'SoS', Ken