That is certainly the primary goal of the legislation but reasonable secondary goals might be to reduce uncertainty like you’ve mentioned, and also remove scenarios where the punishment doesn’t fit the “crime”. I just don’t see the cost to have included psilocybin but I see the benefit to including it along with these other drugs.

Now you can have 2.5g if meth and show it to an officer with impunity, but the same amount of psilocybin, an objectively less harmful “drug”, could lead to imprisonment. It’s madness.

Also, it keeps the handbrake engaged on advancement of research and development in new psilocybin based therapies.