It would certainly be interesting if they had compared the quality of Mapbox’s traffic data to Google’s. Perhaps the authors tried this and the data wasn’t as good? But it’s not mentioned.
OpenStreetMap itself is just the base map, not a provider of traffic data or routing.
Indeed, and it will be very hard getting anywhere near as good as Google's without owning Android which nobody else could possibly do.
I still think location data collection for the public good should be run by someone who is not Google / Facebook / some other company that doesn't already track everything about you. I'd be happy to send my real-time location to a company like Mozilla or some mapping company (just in the tiny netherlands I know of AND, Geodan, OsmAnd... I'd be fine if any of them organize this).
We also have some open data via the government, based on detection loops in the road, but if I remember correctly it's only (or mainly) on highways.
OpenStreetMap itself is just the base map, not a provider of traffic data or routing.