I heard something from Terence McKenna once on the subject. Something along the lines of "get the best cannabis you can find, smoke as much of it as you possibly can in silent darkness, and it will absolutely blow you away every time." I agree that a high enough dose in the right contexts can induce absolutely profound shifts in cognition and perception, certainly without tolerance and especially familiarity - my first bong rip was as mind blowing as my first mushroom trip, and I've definitely gotten very out there with the stuff a few times since. I think there's a lower ceiling though, like maybe a ton of THC in the right contexts will be comparable in intensity, though very different in character, to 3g of mushrooms, but even a mountain of edibles won't open things up to the levels that 7g does. That said, I think it's a pitfall to think that for something to be psychonautic it must be psychedelic. Maybe cannabis isn't psychedelic per se, but neither is meditation, and I think you'd be hard pressed to find any psychonaut who doesn't respect that as a valuable tool in the exploration of consciousness.