This site has such depth and quality, I'm pretty sure you can do whatever you want. The ratios won't be that much higher once people start going for those easy DLC achievements. You'll just make gaming companies that much richer. Isn't that a good thing?
Don't get me wrong, I totally understand the anti DLC attitude (I have it as well), but this system is just living in denial. Hey, I love the site and whatever is done is fine with me, I'm just intrigued by this debate.
Oh yeah, I understand that rarity is THE only mathematical way to track difficulty. That's why I love this site so much. I apologize for bringing up what appears to be a sore subject, I realize I'm just a lowly door person newbie.