With respect, the warning horn thing was well known before Helios 522 and had been subject of accident investigation recommendations to change (Norway in 2001 and others). NASA issued a special bulletin on it in December 2004 and another one after Helios 522. Implicitly they were warning that if something weren't done something very bad could happen -- Helios 522 was it.
Boeing refuses to change it, relying on "grandfather" clauses to persist with a warning system that would be permitted on no new aircraft design. It is not a question of endlessly adding new warnings, but of getting rid of bad ones and conforming to modern manufacturing and design standards. And as for the human factors issues, competence etc,. it is a truism that, as remarked above, the best pilots can have the worst accidents. The critical path here is about accurate and unambiguous warning devices, not training or airmanship deficiencies.