Proposing this as a viable alternative would require a very high amount of evidence.

I don't see where you got the idea that it's supposed to be an alternative. If I'm less clingy because I have a Tupla and thus no fear of being alone I have an easier time interacting with other people.

Proposing this as a viable alternative would require a very high amount of evidence.

There are much bigger claims on this side with much less evidence. Just look into discussions of uploading and AGI.

Nobody hear advocates that it should be standard procedure to train every lonely person who seeks help to have a tulpa.