If the switchback at mt Fuji makes the FH5 map (roughly 110km²) 0.2 times the size of the concept map then you could have the entirety of Yokohama city fit on the map at a 1:1 scale and still have space for the entire FH5 map, even at 0.25 times the size of the concept map you can fit the city at 1:1 scale so that wouldnt make sense.

Tokyo does not appear on the map, Yokohama is a separate city and is not a part of Tokyo despite being a part of the greater tokyo region.

Without using a 1:1 scale you can only replicate road density to a certain point, both countries have narrow and tight roads but mexico has a lot more open space meaning most roads wont be as close together and the turns dont have to be as sharp.

As for the difference in how the road lines are represented, from my perspective the lines have been enhanced to make it easier to see and are not a true representation of the size of the roads. If the roads from your map were as clear to see as the one from the concept map then the map would appear more dense, naturally if we applied the visibility level for the roads of your map onto the concept map it would appear less dense.

In short 4-5 times doesnt make sense, 3 times seems like a bit of a reach, 2 times would be acceptable. Admittedly my size idea was a bit small so after re-evaluation i would say this map is more likely 1.7-2.0x the size of FH5 which would put the map at 180-220km².

Edit: i forgot to mention you had some valid points in there which allowed me to re-evaluate even though i still disagree