>neanderthals were "outcompeted" because homo sapiens had language
I think any small groups of humans were just one virus away from extinction. Even we almost disappeared. A species that has a very low population for the entire species then all get sick that is bad even if all do not die. Your species loses genetic diversity and then another virus or even a large natural disaster strikes the group wiping it out. Maybe we just were lucky and survived not due to any skill better than other species.
I think any small groups of humans were just one virus away from extinction. Even we almost disappeared. A species that has a very low population for the entire species then all get sick that is bad even if all do not die. Your species loses genetic diversity and then another virus or even a large natural disaster strikes the group wiping it out. Maybe we just were lucky and survived not due to any skill better than other species.