This has nothing to do with open source. For GraphHopper I researched many papers regarding fast routing algorithms or advanced data structures etc ... and I'm

This has nothing to do with open source. For GraphHopper I researched many papers regarding fast routing algorithms or advanced data structures etc ... and I'm pretty sure that this is true for other open source projects too. It could be even the opposite: because many people can look into the code the code converges to the state of the art.