I never even implied someone was a poor musician. They do however, perform poorly. I believe this because I've experienced it again and again in different decades, genres and with musicians that play different instruments. I know it's the dope because I've had rehearsals with the same musicians when they were straight and they played great.
Here are 2 examples. Great guitar player. Studied with Pat Metheney. Played great. Original band. We eventually told him not to get high on stage because his playing suffered. He stopped.
Drummer. Same situation (no Pat Metheney). He wouldn't stop. Fired.
These occurred 3 decades apart.
There may be musicians that were stoned, drunk or on something every time I played with them so I never knew the difference but I doubt it.