If you want reports on the behavior of Aleut and GP in various scenarios, you can start reading over at qajaqusa.org, there's a wealth of info there, most of it very well reasoned and perceptive.
Per your logic argument, there are generally multiple solutions to engineering problems. Neither the GP or the Aleut is a single design --- GP and Aleut paddles, with their wide spectrum of sizes, shapes, etc represent a family of solutions to the paddling problem. To pose them as competing designs doesn't seem particularly useful.
As far as the intentions of the builders in crafting a ridge on a paddle, of course that lies shrouded in mystery. From the standpoint of low-speed fluid mechanics, however, the behavior of the ridge in determining the flow pattern over a paddle is not really an issue of trust, but of analysis and observation.
As far as the effect of the ridge when slicing the blade or rolling, I don't remember reading anything about a difference between the two. The difference may exist, but I wager it's subtle, otherwise it would be talked about more often. If it was a real drawback, I bet the Aleut would have discarded the idea --- after all, being able to roll successfully is probably more important (as in life-saving) than avoiding flutter.
Free Standing Boat Racks
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