That's probably true. Decriminalization is an imperfect first step that can be taken unilaterally by the executive branch while the legislative is deadlocked. In time society grows accustomed to decriminalization and the true legalization is more feasible.

In California the decriminalization of magic mushrooms has caused lots more people to start growing them, so price, quality, and diversity are better than ever. That probably wouldn't be the case with other drugs that aren't as easy to produce just anywhere. Although opium poppy field or coca greenhouses are definitely possible.