I don’t have any personal experience with psychodelics, but I would believe they could do that.
I do think it’s important, though, not to be too seduced by oneness. As you said, there are many ways that one can come by an experience of the whole—meditative practices, chemicals, even strokes—and that experience does have great value, no question. The idea of oneness doesn’t change lives. Oneness has to be a gut-level experience to have transformative power.
That experience is wonderful, primarily because it brings such relief from all of our psychic distress related to isolation and incompleteness. But there is a certain danger of getting too enamored of that experience. This often happens when one has this experience with no context or discipline to give it perspective. It can seem to stand in stark contrast to the “ordinary” realm of experience, and be cherished as something special and more precious than ordinary experience (that’s the vibe I get from listening to Bolte Taylor talk).
But that is just as much of an imbalance as being stuck in discrimination. The needle has just swung to the other side of the dial. That’s a more pleasant state, to be sure, but it ignores some important aspects of human life, and so it’s delusive in its own way. Understanding this is just as difficult, and just as important, as getting that insight into oneness.
In the end, oneness and differentiation have to be integrated. They have to be seen as inseparable partners in reality. Then, differentiation is oneness, and oneness is differentiation. They don’t stand in opposition. It’s highly unlikely that a stiff dose of ‘shrooms will lead there.