How does that affect the question of whether the network is densely packed or whether it has frequent trains?
Passenger trains from Frankfurt to Cologne are infrequent because there is virtually no demand to move between cities 120 miles apart. Because the trains are infrequent, they aren't dense on the tracks.
But that's the opposite of saying that they are frequent and densely packed.
Read up on what affects railway bandwidth. A densely packed 250km/h line won't appear similar to a densely packed subway line to a bystander despite of maxing out its abilities.
Trains inside cities (i.e. trams and subways) are much much more frequent because they have fewer constraints and lower speeds.