In Shanghai, using Uber's carpooling feature it is much cheaper to take Uber than Didi. I have had quite a few rides (with 2-3 other people riding with) that were cheaper than it would have cost to take the subway. I'm not sure Didi has the algorithms ready to do this yet. I should say I haven't tried Didi in a few months, it may have improved since the last time I used it.