I was recently kicked out and blocked by the British Bigfoot Facebook group for suggesting the "British Bigfoot" is not a flesh and blood entity but possible a tulpa or a manifestation of an archetype. They really don't want to entertain any ideas other than it's a flesh and blood beastie.
I think your line of inquiry into tulpas and archetypes is unfairly dismissed Mouldy13, though I could also understand how a group dedicated to the gigantopithecus theory of Bigfoot might feel it was a distraction. I thought I should offer you a bit of supporting evidence for your idea, as it has crossed my mind as well.
I recently listened to an episode of the podcast "Sasquatch Chronicles" entitled "The Quantum Bigfoot" which discussed some of the seriously supernatural things that these creatures can allegedly perform. They seem to be able to defeat not only the visible light spectrum, but also interfere with electronic equipment at a distance if the stories are to be believed. It is all a bit reminiscent of the faeries in Eoin Colfer's "Artemis Fowl" series of children's books. IDK if you are prepared to add faerie to the tulpa/archetype list however. Me? I think it fits, but I would add more...
In Japan they have a lot of odd local spirit creatures called "Yokai", and there is one in particular which is pertinent, called an "Otoroshi", often described as a big hairy man who frequents holy places. Now interestingly, elsewhere I read that before the Blessed Virgin Mary is sighted in an area there are prior sightings of a big hairy man in high places on the local place of worship.
Now another line of inquiry is the Cult of Pan. Another big hairy man of the wilderness. This fellow emitted a terrible cry in the wilds that drove people into "panic". Many witnesses have spoken about the chilling cries of sasquatches in the wilderness. To me, that seems like a good fit.
It also occurred to me that if there are any legs to the Smithsonian Giant Exhibitions conspiracy theory, perhaps the giant humanoid remains in question were actually sasquatches?
I hope my wild suppositions on this subject at least amuse you. Note also my restraint in not once referring to Nephilim or reptilian overlords.