For that to be true the AT-ML170/180 would basically have to be the best cartridges ever made, by some margin, as to my ears the 150MLX/Sa are both reasonably close to being state of the art. Maybe they are just that, as I've never heard either, but I kinda doubt it. Or at least I doubt that it is anything even vaguely approaching an objective fact.
@agrippa They are the best, unfortunately all audiogon users who actually have them and compared them are not active anylonger here and instead we have just the basic recommendations for usual suspects.
The difference between MLX series and vintage AT-ML series is obvious, the cantilever is completely different, the moving mass is different, the frequency response is different ... and so on. They are from the same manufacturer, but different legue.
Highly recommended if you have not tried yet, even AT-ML150 with Beryllium cantilever is a killer MM (cheaper than AT-ML170).
The AT made a lot of cartridges, my first one was ART-2000 MC, it was $600 cartridge (limited edition) and i was blown away. But the AT-ML series is much better. I am a big fan of AT, it depends how far we would like to go in upgrade. In case with MM it's better to go backward to the 80's.