I believe cocaine is a bit easier than meth, though I'm no chemist. In any case, you're certainly right that it wouldn't kill the black market, but it would still weaken it (I edited my post on this point, sorry for the confusion).

If you can get an ephedrine compound a synthesis for meth is possible where you just throw everything in a pot and come back to it. Small scale production used to be fairly prolific based on total consumption. That said its total production volume in that manner was low.