Calling 'consciousness' 'soul without an afterlife' is just as much a word game as any other - which is to say that if it is offered as the starting point of a discussion, it is not simply a word game, but if it is declared to be the answer, then it is.

I don't think the circularity is there, because while there do not seem to be other animals today with the same sort of consciousness as humans, we can reasonably assume that some of our now-extinct ancestors had various levels of consciousness, whatever it is.

We are indeed groping around here like 18th-century scientists trying to make sense of heat. I don't think that makes it pointless, but we should be suspicious of the claims of either physicalists or dualists who think that they have proven the other side is wrong (though my instincts are with the physicalists.)