I don't really think the Oneness has anything to do with channeling. Keep in mind that while Rand learned it, and some male channelers find it useful, it is actually very different from the sensory amplification that the Power gives you. Think of it like actually using all of your senses and becoming fully aware of your surroundings versus becoming hyper-aware of them. Lan never suggested he could make out every crack in a fortress' wall, see every possible hue of the various colors or even hear people breathing, but channelers can.