Not my "assumption"--it's a reasoned argument, based on the legally sanctioned "tipped employee" rule. You don't have to agree with my reasoning or my conclusion, of course.Yes, I absolutely disagree with that premise, and your view of what the employee's work is worth is just your assumption starting from quite a different viewpoint than what I and many others have. And it absolutely is a gratuity since no customer is legally obligated to pay it, and the employer is in fact legally obligated to pay any shortfall from the regulator minimum wage. The fact that some customers may feel an obligation to pay is a misunderstanding on the customer's part (or guilt, or virtue signaling, etc.), rather than a real obligation.
As for whether it's a "gratuity," a "tip" in the US does not meet the dictionary definition of "gratuity." If it says "gratuity" on the bill, that's a misnomer. I disagree that the customer's feeling of obligation to pay is a misunderstanding on their part. Rather, it's an acknowledgement of the social contract we have created in the US among the employers, their tipped employees, and we the customers. No, it's not a legal obligation; rather, it's something implicit we have created, gradually having morphed into what it is today. But the "tipped employee" rule leads me to my conclusion that it really is more like an obligation or contract than a traditional gratuity.