All fair points but what I did mention is a real thing too. Of course there's different qualities of different drugs, I didn't mean to say there aren't. Yet there has to be a dozen threads on BL alone with people asking same question about different substances and I guarantee you if you wait long enough you'll see yet another about Meth before too long. A prime example is this thread
https://www.bluelight.org/community/threads/what-is-wrong-with-the-mdma-available-today-v2.895430/ which has 154 pages on the 2nd iteration of the thread because the first thread reached it max limit of posts. If you go through that thread you're going to see the same arguments and beliefs over and over even when most of the science/lab analytics tell us that MDMA today is largely the same as MDMA of the past. I'd even posit that the methamphetamine argument you made about a lot of meth being racemic vs. the pseudoephedrine route which produced purely D meth has some merit. MDMA has always been produced racemic, all of the newer precursors and synthetic routes for the vast majority still go through the intermediate MDP2P/PMK and you're still gonna have people insist that MDMA just isn't what it used to be, period. And you will have people who say the same about most drugs including meth.
I was really pointing out that there is a very real tendency for people to be nostalgic about when they were actually enjoying the drugs in their hey day of usage and it will just never be the same for them.
And one thing about meth as you said vast majority of it is being cranked out by super labs in mexico where they probably do make a relatively consistent product. People cutting drugs when they hit the street is a different thing.
Yeah it was a bit arrogant and broad speaking my bad. I certainly know a lot less about methamphetamine but I will tell you that I worked for an analytical laboratory where I've tested hundreds of samples of MDMA and also relatively common were black market adderal pills which were almost always methamphetamine. We did not have a polarimetr which would help us identify isomeric ratios so I can't know much about which isomer the meth/aderall pills were. With MDMA almost no one is isolating one isomer over the other.