Okay, let's try this again.
Packages that have conflicting resources will be installed in such a way that the highest numbered package (in the order list) wins. Those resources will be the ones that show in the game.
Newly added packages (archives) are added to the bottom of the order list. Just before the "Last" marker/separator.
Wrye Bash is coded so that you can manually move packages beyond the "last" marker. Because newly added packages are added _before_ the "last" marker, any packages that you manually moved beyond the "last" marker will NEVER have a newly added package over-ride them.
That's the purpose of the "last" tag. It's for people who don't fanatically sort their packages every time they add a new one. I don't for one, unless I think it's important.
I don't care if you disagree with me not sorting my packages every time I add a new one. I don't care if you don't think it's a good use for the "last" marker.
That's what it is for. It does what it is for properly.
If you want a new feature, request it. Just accept that the "last" marker is doing exactly what it was meant to do. It's just not doing what you wish it was meant for.
Edit: I am trying to understand the functionality of that marker. The only thing I know is that newly-added packages are put above it.
That is the entire functionality of that tag. It designates a place for newly added packages to be placed so that they don't over-ride packages that come after the "last" marker.