Having a flashlight on your bicycle as part of an optimal night riding safety system is a great idea. Using a flashlight as the primary head light or "only" light is patently ridiculous.

When I used to go on my all-night century rides I would lash a powerful 1000 lumen flashlight to my handlebars using an old bicycle tube as giant rubber band. If I encounter oncoming traffic that would not dim their headlights I would turn the flashlight to high power at tip it directly at the oncoming vehicle. (they usually dimmed their lights after this)

In addition, I used a helmet light to attract attention of motorists at intersections or driveways. An helmet light is a necessity on unknown routes - you can use to read road signs as well as identify hazards coming from off road areas.