I agree with you that you can take the ratings for many of the Chinese made lithium ion batteries with the same "grain of salt" that you can take the ratings for many CREE XML-T6 flashlights sold on eBay. The flashlights can't be more than a bit over 1000 lumens as that is what CREE says is the maximum output for the T6 bin.

I will speak out in defense of the cheap batteries. I've used them myself for a flashlights and some DIY LED bike light projects. If you want an inexpensive but workable battery, they are a very cheap alternative to the expensive throw-away alkaline batteries like Duracells. The Panasonic 18650 batteries on eBay run between $6 and $9 each including shipping. Most of the Ultrafire and Trustfire batteries I used or gave away as gifts with flashlights were around $1.50 each. Six bucks to make a 12V DIY battery pack sure beats $24. I don't expect them to last as long but for a buck fifty, who cares. Nobody has complained about being given bad batteries in the flashlights I gave to friends.

Even within the same brand (Ultrafire) there can be a pretty large difference between the weight of their batteries and it doesn't correlate with the mAh rating:
Ultrafire BRC 5800 mAh 27.8 grams
Ultrafire BRC 3600 mAh 31.9 grams
Ultrafire JYD 5800 mAh 27.6 grams
Ultrafire BRC 4000 mAh 37.3 grams
Unbranded INR 18650 2000 mAh 42.6 grams
Unbranded purple case 4900 mAh 40.9 grams