I've also had issues with Transit surfacing incorrect bus routes based on cancelled buses (but scheduled) which CityMapper somehow could account for. Transit knows the next scheduled bus two minutes away isn't "live" (icons are different) but still surfaces it as a primary suggestion, while Citymapper wouldn't.
The crowning feature of Transit is the GO trips that let you share you location while on a bus with others. For bus arrival accuracy there’s nothing better. It’s probably saved me a flight or two before, by just making sure I get the 747 bus to the airport.
i do like that the departure times are (slightly) more accurate because of the crowd-sourcing. however, the underlying data from metro is a mess, so they end up looking bad anyway because trains and buses still show up (or don't) unexpectedly due to metro's unreliable data.