Yes, I also believe that, in the US at least, the social pressure distorts the signal that the tip sends so it's meaningless. There is such a huge stigma associated with not tipping (or tipping poorly), that most people will tip a decent amount even for poor service.
Granted, the rating system is no better, even if for different reasons: since Uber/Lyft will deactivate drivers if their rating falls below what I'd consider to be a fairly high value (something above 4), most people (where I live, at least) give 5 stars unless there was something seriously wrong with the ride, so a mediocre driver will get the same rating as an exemplary driver.
If pulls a 5-star service for 499 customers and a 0-star service for a single customer (for whatever reason) his rating drops from 5 to 4.99, which doesn't seem that relevant. Unless a 0.01 drop in his rating means a loss in earnings greater than that of a lost tip, the tipping system would provide better rewards for not dropping the ball.
Forgot about the social pressure, too (I'm not American). That could be a real issue, because if people don't actually consider not tipping then it's just dead as a incentive scheme. They'd have to make tipping anonymous.
By the way, I don't think pressure under anonymous choice is "social". You could attribute it to education and thus society and some way but ... that's rather roundabout. I think the more appropriate term is "consciousness".