I would argue that although the context has indeed changed, embracing Stoicism involves far more than retreating into the mind and simply accepting what one cannot change. It is far, far more than that. It is about freeing the mind from this Big Other you describe, and it describes detailed practices in which one can engage to achieve this end. Stoicism doesn’t try to find an area of freedom in the inner world, it succeeds in doing so. Perhaps the modern context has simply made it more difficult to pursue considering the sincere, wholehearted effort required in such a journey.