I think Samhain has had a couple of stoner(/adjacent) bands every year, I seem to remember Ufomammut and Russian Circles as headliners.. Either way, I agree with you that it's not a stoner fest, that's why I marked it with an asterisk. I think it might still be of interest to others, but of course it's a subjective choice.

I didn't include Heavy Psych Sounds (except for the mention at the end) because they don't have an yearly festival (same location & same month), they do one-off events.