Amsterdam is miles ahead in terms of infrastructure. This ranking dilutes the most important thing to get these results : good bike lancés everywhere with no discontinuity.
Disclaimer : I've built villes.plus, an open source automated evaluation of bike lanes. 100 points, compute itineraries in "secure" mode with Brouter between these points, count the % of secured km -> score.
Amsterdam tops at 8/10. Bordeaux is at 3/10, Nantes 2/10.
Dutch urbanists have found that bike lanes are very important when streets used by cars are unaltered. Once you implement a lot of traffic calming features and cars never reach 30kph comfortably, bike lanes aren't that important and then streets can be shared across all users.
Of course it is. See % of safe km as a minimal condition, not as perfection.
Note that bike lane ! = safe km. You're right. There are bad bike lanes and good peaceful streets. See other comment for algorithm.
20 km/h streets are counted.
Amsterdammers prefer to think of themselves as kilometers ahead. ;)
Feel free to suggest a better algorithm ! It's version 2, issues already discuss missing important OSM tags.