Apart from demonic and angelic ontological cores, what are some other kind of beings that have incarnated as humans? I used to be really into New Age spirituality and so believed for a long time, as it is 'preached' by many channelers, that most of humans' souls were actually extra-terrestrials, but you've said that it isn't the case, so a lot of these people believe to be aliens when they aren't? Even though they claim to have 'channeled' that info?
Indeed, many people claim to channel when it's simply their own imagination telling them while they close their eyes. Unfortunately nowadays everyone can claim everything on the internet, and there's great difficulty to tell what's true and what's false. I am not saying that they mislead others on purpose (although this happens as well); but they can be deceived by their wishes and desires, and they can seem to have any sort of confirmation in their minds, regardless of the truth.
The most basic premise for an incarnation is the purpose for such a thing. This is due to three factors: Debt (Karma), Lessons, or Mission. If what they claim was true, then why all those extra-terrestrials are born here all of a sudden? Surely not for Debt. Lessons, doubtful, since they believe they can teach others, therefore they claim to have superior wisdom. Mission, perhaps. But even that should be enough for anyone to see that if the majority of the human souls were on a mission to save humanity in some way, we would have no wars, no envy, no greed, no strife of any kind, simply because it would be the collective will of the majority speaking. Instead of this, we have this world, full of injustice, inequalities, violence, and several other problems. So everyone can see that most of the people, including their elected governments, are not so wise and illuminated after all.
Apart from angelic and demonic cores, there are some dragons still entering human bodies (but it's a minority), and also elves (who are quite a lot). There are some even smaller subgroups, but the problem is that as soon as they are mentioned, suddenly thousands claim to be them. I am not saying that it is impossible; I'm simply saying that the numbers they claim are grossly exaggerated. The majority of the Earth's population are humans; human cores (psyches) living in human bodies.