Try using the tag;
[Series]=[]
That can be saved in the tagging rules, and I think it will work.
Note that CARNAC happens before the tagging rules during Import, so it has finished its job and assigned whatever tags it thinks it finds in the file name before the Import tagging rules are applied. So the [Series] tag is set before MC see the [Media Sub Type] set to "Home Video". CARNAC is fully automatic so you can't stop it doing that. Fix it with the tagging rules as you have been trying to do.
You can also use the [Filename (path)] and [Filename] tags to move the files if you want, perhaps to a subdirectory on the Home Videos directory called [Gallery], if you wanted.
i.e.
[Filename (path)] = D:\Home Videos\[Gallery]\ (don't forget that last backslash!)
or
[Filename] = D:\Home Videos\[Gallery]\[Gallery] - [name] ([date]).mp4 (or some variation you wanted to use.)
If you do use those, put that tag as the last in the list.