As I understand it, in the UK RTTI traffic is provided by TomTom, as is the mapping data. In my experience TomTom traffic is superior to google traffic.

However, it doesn't matter how good the traffic data is if the navigation sw doesn't know what to do with it efficiently. Like you say, idrive nav makes some poor routing decisions.

I've had TT and idrive nav running alongside each other. Both show the same traffic delays, updating within a couple of mins of each other (same source). The difference is that TT makes logical rerouting decisions, and idrive more often than not, just drives you into the known traffic, or reroutes inefficiently.

I don't rate google maps for in-car navigation. It's free and has amazing points of interest/mapping, but the visual display is confusing, no speed limit info and no speed camera info. It also has very limited configuration. I used it in Crete on hols and it was awful. The road names are long so it would often be 30 seconds behind with audible instructions, directly conflicting with the visual instructions. Other navs allow road name pronunciation to be turned off. It also only used about 10% of the display for the actual direction mapping and the rest of the screen was wasted. I think this is a regional issue as it doesn't do that in the UK, but it made navigating with it almost impossible. TomTom on the other hand was a breeze.