It's up to your manager to determine who is a good bartender and should be rewarded extra, and who is not. That's not up to me, and I shouldn't have to bother with trying to judge others on their performance. I hate playing the, "is this bad enough to take away money from them" game. Just give me a price and let me pay that price. If I have a serious problem with someone I can contact the manager.

Plus, many many many service jobs exist without tipping, they still do a good job. You act like tipping is the only mechanism available to incentivize and manage employees performance. Most of the working world is untipped, and somehow good employees get rewarded and bad employees get punished. Plus tipping is provably sexist as a means of income because women naturally earn more than men. It doesn't reward good performance, it rewards bust size.