Duplicates exist so you don't get everything you can unlock in 5 days. If you, for example, have all the vanilla CoH2 content, and duplicates didn't exist, you'd get all the unlockable WFA items in a few days.
Actually it would be just like the original system. We would unlock things bit by bit, over a series of weeks/months (depending on how often people play). There is plenty of extra bulletins, etc for the add-on to mean it will take more than 5 days to unlock it all.
If they wanted it to happen more slowly they could link items to certain progress levels. Or better yet they could have simply kept the original system - especially as that actually had a built in anti-farming system, as it was linked to progress, which is generated by XP rather than time.
Basically to fix all of this and still provide the free content, which they claim to want to give us, all they need to do is re-introduce the old system.