That's a fair point, but we should also note that the mighty thinker Aristotle speculated seminal theories of relativity, continental drift, and evolution. I mean Freud's discovery of the unconscious as OP presumably means the discoveries of Einstein, Wegener, and Darwin respectively. Freud's scientific conception of the unconscious was a breakthrough beyond his progenitors.

I'll only admit I've cheated a little: that Freud's contribution was a scientific one is not an assertion that is "generally regarded as correct." But Freud believed himself to be a scientist and frankly I agree. It's not like Einstein, Wegener, and Darwin are uncontested figures, but certainly Freud is much more so.