Take a piece of tin, or brass shim stock. It's floppy. Bend a crease down the center like a pitched roof. Now it's much stiffer. You've increased the cross section. Now instead of .030 thick, it's maybe .500 tall from peak to base depending how far you creased it.
You've essentially created a triangle in the material in the axis of the stress. Rather than the flimsy flat with it's two points or lines of stress, you've added a third and moved them apart 5 or ten times their original difference. That distance is like a lever of support.
I'm not trying to say you can't do this with a fuller as we discussed. If you just move the material into a strategic location like the bend in the shim stock, it has a similar effect.
I'm trying to describe the scale is vastly different. If you take a .200 thick blade and fuller then upset the spine into a short "t" you'll maybe increase it to .250 or .300 at the most. So rather than increasing the cross section by 5 or 10 times, you've only increased it by 25 or 30%.
That's why a tape measure acts so stiff, but the simulated blades with fullers and equal mass only showed a small amount of deflection resistance. So yes, similar effect to creases in sheet steel to prevent oil canning, but at a vastly different scale.
I hadn't even considered the effect that geometry might have on vibration and think that's a very keen insight worth investigating further.