Given that tips are a percentage of the overall bill, could you explain the potential performance difference between pouring a $7 bottle of wine and a $700 bottle of wine? Assuming that the customers already clearly know what they want to purchase, so the waiter didn't offer recommendations of any kind.

But even if we take that last point into consideration, a good waiter that cares about their customers can offer a cheaper, more suitable bottle than something expensive. How can they receive a higher tip than the person who does not offer suggestions but merely pours a more expensive bottle?

This is not even mentioning that the baseline of "performance" is sub-par indeed. Americans tend to gloat about how their tables never receive water top-ups or someone never asks how their food is going so they have an opportunity to ask for condiments or napkins. But most people in the world typically know how to ask for themselves if they require something, and don't need a pseudo-butler hovering over them. Not to mention that when it comes time to actually pay the check and leave, Americans tend to be some of the slowest at actually fulfilling this process.