Is the expression “the biggest such business” grammatically correct?

1. I have found the expression “the biggest such business” in the second sentence in “The Economist.”

https://www.economist.com/china/2018/12/15/the-west-once-flooded-china-with-opium-china-is-returning-the-favour
It has also made it easier for people to find the ingredients, kit and talent necessary to cook them up illegally.
For years the biggest such business was making stimulants such as amphetamines and methamphetamines, which are also produced in neighbouring countries (see article).


2. So I tried to find out how to use “in what order to use ”such“ and ”a superlative.“ and I have finally found the following.

https://forum.wordreference.com/threads/such-with-a-superlative.3265502/
I think you mean before an adjective rather than after it -- but no, you can't follow "such" with a superlative.

3. In conclusion, both statements are contradictory to each other.
So which is a grammatically correct expression on the basis of English gramma books?