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It's not about having everything unlocked, but knowing if the system works. Assume that you had everthing unlocked prior to WFA, then you'd have roughly 50 new things to unlock. This would make the chance to unlock something of those really small, so you might play 100 games without unlocking something (and at that point people usually go to the forums and complain it's not working). If you unlocked more, the chances are even smaller. I think I calculated it once that for the last few items you need roughly 500 games each.
Duplicates allow people to see the system is working (or well.. would've had it been known earlier that duplicates are fine) and makes it easier to add features for them later on.
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Then don't freaking buy them. Honestly, you just want to complain, right?
In another thread you complain about DLC commanders now being unlockable simply by playing, making you feel like you've been scammed. Here you complain about the exact opposite, that commanders you do not have, but are available for drops will now be able to be bought.
Either the drop rate is so high, you do not need to buy them (then stop complaining about the DLC, nobody forces you to buy any) or the rate is so low, that your earlier complaint is invalid. I know that not everyone is happy with every solution, but if people contradict themselves? That's when it starts to be really annoying.