I think there was truth in what he said. But losing 40% in a wash is bullshit and a sign of very poor quality. When I washed meth from my usual source I would usually lose only 5 %. Even washing the stuff I got from my sketchy backup street guy in an emergency only lost 10-12 %.
Does the wash get rid of caffeine exclusively? Or do more of the other common cuts (like sugars) dissolve too?
If it did wash out more of them, then I guess your speed would've had a purity of 60% or maybe a little shy of that? I don't know what your vendor advertised, since that really determines if you got ripped off or not. But the standards for sulphate seem to be totally different than crystal
For the former, low purity appears to be the norm. In most European countries, the median purity of a gram bought on the street in 2019 was 11-15%. And that reflects a big improvement over the last decade, over a 60% increase from the turn of the last decade, when purity in the UK was hovering around 4%. (For comparison purposes: 1 gram of speed at 11% purity has 55mg d-amphetamine; at 15% purity, it has 75mg of d-amp.)
Some countries, like Belgium and Sweden (no surprises), lead the pack with sustained 25%-30% averages (not just single-year possible-flukes), but even the best product around tends to be diluted somewhat. The UK's purest single sample in 2019 was 67%; in 2018, only 52%. I remember reading that UK purities peaked around 20% in the mid-90s, so it's likely that they've been down for a while in all of Europe.
Even within a continental context of low-purity amp, the EU meth purities are way higher across the board, in countries where it is dominant and where it -19is8 not. During the 2010s, Czezchia's median purity was continuously above 70%, while Austria's ranged from 57-73%. It wasn't uncommon to see street-gram purities reaching up even higher.
France is primarily an amp sulphate country, but their meth hit the 80% threshold twice in the 2010s [with most of the other years at 76-78%]. And in Turkey, where meth is predominant (and blowing up ATM), the top year for purity was 2015 with 86%, but three other years in the decade hit 80%+.
So in conclusion, I guess your speed was pretty good after all, at least if you put it in context (and assuming there's no false advertising). If "only" 40% of the weight was diluents, the strength was certainly way above Euro standards. Hell, you oughta enter it into the 2021 UK Strong Phet competition, probably would've made runner-up two years ago.
But it's also completely understandable why you were nonplussed, given the norms for meth. I don't know why the disparity is so huge, but I do know that amphetamine in most of Europe has been launched down the sad slide to anachronism by cocaine in the last two decades, quite the opposite of crystal meth. Did the lower purity level result in a low popularity level? Or was it unpopularity that lead to unpurity?