Well, I disagree with the idea that a randonneuse is "...for casual riding with a handlebar bag from village to village by a rider smoking a pipe, without any atheletic pretensions whatsoever." At the time (40s through 60s, or thereabouts), the top finishers of the famous brevets were almost universally mounted on what we now think of as the traditional randonneuse. Many records were set on these bikes, with their light weight, "racing" tubesets, etc. Today we see fenders, front bags, wide tires, etc. and think "slow" but when you are riding all day and night, without resupply, in the rain, over lousy roads, those "slow" items make a big difference in how fast you can go while minimizing stops. Even today, folks like Jan Heine are "winning" brevets and setting course records on these bikes.
Just because I'm a lard-butted pipe smoker riding from town to town with no athletic pretensions whatsoever doesn't mean my bike isn't capable of a whole lot more!