It seems to me that the Elephant in the room is not the racemic composition of meth, or purity, but composition and nature of the remaining impurities.
Do you know if these are well understood and tracked over time?
I can't rule it out, but it's unlikely. Unless the meth cooks are doing something really bizarre, it's unlikely anything in the synthesis route produced as a side product is going to be as biologically potent as the meth itself. (This is not true for other street drugs, see MPTP). P2P Meth synthesis is pretty simple and straightforward if you have the reagents, it's Organic Chem 2xx-3xx level stuff. And it is really easy to crystallize to high purity.
I think it's actually the opposite of impurities. The tech and supply chains have gotten so good, the purity had gone way up and the cost down, that people are just using way more of it.
Do you know if these are well understood and tracked over time?