Some airframes that are optimised for external load work (for example, K-Max / Eagle Single 212) are single engine by design / modification.
Does this make them inherently unsafe or does the improved power / weight ratio make them better suited to their intended task and potentially safer if they can maintain an increased thrust margin?
True twin engine ‘safety’ for external load ops only exists when you are assured single engine OGE performance - the weight penalty to achieve this is probably so restrictive as to frequently make it functionally impractical (as well as economically unattractive).
Cost is undoubtedly one aspect of the equation, but actually being able to complete the task at hand is surely a consideration too?