Your system works because your tours are evidently limited in nature and you do extensive pre-trip planning and you seldom or never deviate from your meticulously planned route. Many people plan their tours on the fly and a small GPS device will be cumbersome for this compared to a paper map. Even a full-size computer display is cumbersome for planning purposes compared to paper maps. Also, your routes are evidently either very complicated or you lack short-term memory and you are fascinated by the idea of never losing a minute of precious time by having to stop at an intersection to check which way to go. You also don't apparently have to make a tradeoff (money or weight) with regards to how many electronic gizmos and spare AA batteries you will be carrying on a long tour. In other words, you are quite different from the sort of bike tourists I'm more familiar with.

Where GPS (mapping or non-mapping) really shines is for hikers going cross-country in featureless but rugged terrain, where topo maps plus compass are next to useless for finding position, especially when deviating from the desired route is dangerous, such as due to the need to cross a river at a particular spot where it is known to be shallow. For traveling cross-country on terrain obscured by snow, in particular, whether on foot, skies or snowmobile, GPS is a god-send. Bike tourists (this is the BIKE TOURING forum) almost never encounter situations like this.