I'm sitting at 4.97 in LA - but I ride a lot. And my ratings scale for drivers is similar - 5 star for normal, compliments for things above that, <4 stars for "you did something obviously wrong, WTF" level service.
As for racial / protected class bias in ratings - I'm not sure what Uber would hit that something like Tinder wouldn't, since all the ratings are from other "users".
Posting racially-discriminating for-rent ads gets both the landlord and the newspaper in trouble. "We're just a platform" doesn't work as an excuse.
It's also not hard to detect statistically - with enough data you can see that a given driver is giving worse ratings to protected class members compared to similar drivers at the same time and place.
Riders can self-select into a protected class, maybe?
This will of course lead to a situation where some hooligans opt into a protected class just to mess with the system. Even still, on large number of rides it will even out.
But everyone is a member of a protected class. Some people might not be members of historically disadvantaged protected classes, but the relevant laws don't discriminate in that way. ('Men' is a protected class. 'Women' is a protected class. And 'Other' is a protected class, too.)
There's no such thing as protected classes in dating though, so I don't think it's a useful parallel. You're allowed to not date, say, people of other races if that's how your tastes run, but you're not allowed to discriminate against providing business services to people by race.
Is showing your profile to other people a "business service"? Because IIRC Tinder does some ML to show you people they predict you'll like (based on what other people with preferences similar to you liked) - and that would probably result in showing certain profiles to others less often.
As for racial / protected class bias in ratings - I'm not sure what Uber would hit that something like Tinder wouldn't, since all the ratings are from other "users".