Final answer:
The primary drawback of public relations-based messaging in the marketing mix is the comparatively little control a company has over how its information is presented to the public once it is handed over to media channels.
Step-by-step explanation:
The main drawback of public relations-based messaging compared to other elements of the marketing mix is c. comparatively little control.
When using public relations, a company releases information and relies on media channels to publish or broadcast that content. This can be a disadvantage as the company has limited control over how this information is ultimately presented to the public, if it is covered at all. Unlike advertising, where messages are crafted to the finest detail and distributed exactly where and how the company chooses, PR involves convincing journalists and editors to cover the story, who may then interpret and present it differently than intended.
Additionally, messaging through public relations can be influenced by external factors such as current news, public sentiment, and media bias, making the outcome less predictable and controllable.