I guess the main issue about fake blades is their quality control, if they have any. The materials can be different on different batch, and the playing characteristics will be very different from one blade to another.
You do have something correct here. There counterfeiters don't have to make a good blade. They only have to make it look enough like the original that people can be fooled. But, since you said: "I guess the main issue about fake blades is..." I would say, the main issue about fake blades is not that they don't have to make a good product and don't need quality control at all since the only goal is to get someone to buy something that cost about $1.00 to make for enough more that they make money and enough less than the real product that the person thinks they are getting a deal. That is an issue. But it is not the main issue in my opinion. In fact, it is likely that the $1.00 blade that is being sold for $40.00 as a blade that should cost $350.00 is likely to play acceptably well for a $1.00 blade. That makes it so the people who didn't know TT equipment and bought this overpriced but inexpensive racket may never know they have a fake.
I would say the main issue is that you have a disreputable group of individuals preying on vulnerable people who don't know that what they are buying is fake and is not worth 1/40th of what they are paying for it. That, the only reason a counterfeit racket would actually be bought is that the person thinks it is the real thing at a greatly reduced price so the person is being jilted. That is the main issue with counterfeit products and that is also why it is illegal.
The companies that make inexpensive products that don't have as strict quality control in place seem to make very good inexpensive equipment. I would again use the example of the Yinhe Galaxy 896 blade. It is not high quality. It is not expensive. The quality control is not great. And yet it is a great product and it is an especially great product for the $16.00 price tag. It is almost as good as many blades that cost much more. And it is more than good enough for many people. But there is no deception from Yinhe/Galaxy in trying to sell this blade as something it is not. So it is a great value. Whereas a counterfeit ZJK SZLC is a bad value at any price because it is fake and not worth more than $2.00 and most of the price of production has gone into making it look like something it is not.
Nonetheless, Tokeiboi's point is a good one that those counterfeit companies do not need to have any quality control in the actual making of the racket. The main work and quality control goes into making the racket look like another company's product.