Bystander Effect occurs when specific conditions are met and is not just a prevailing rule of human behavior.

The original incident that inspired this phenomenon was shown to be overly exaggerated to reinforce the idea of the inherently violent and apathetic human - which does sell well in newspapers back then and social media now.

If the attack was non-ambiguous, percieved as a high danger/emergency, against the social order/ group cohesion, and bystanders feels competent - do you think you wouldn’t get help? Stop being sold that you are alone and everyone else are apathetic uncaring “humans”, humans legitimately wouldn’t have gotten this far as a species without helping one another.

The bystander effect is a theory, not fact. It can explain after the fact why people in groups feel less responsibility to do something. But it isn’t universally applicable to all assaults in public. There are many variables at play. So “highly unlikely” is an exaggeration in my view.