I consider obligatory 20% tipping as that weird American thing along with guns and (absence of) healthcare. People have elaborate arguments and discussions about them, and the side in favor can look very rational and plausible, and their hypotheses can even have a lot of explanatory power, but they are easily refuted by looking at basically every other developed country.

I travel a lot and eat out a lot and I haven't noticed any discernible difference in service between the countries with obligatory, optional and prohibited tipping.