It seems that they are bending mainly near handle area...... If not, it indicates that there is unnecessary material (and thus mass)I dont think so: The mass towards the outers is mainly needed for stability. If you want your outers stiff by purpose for some reasones then you keep them stiff of course and save mass by making them narrow.
And to me strain mainly is a function of bending radius vs thickness. And if that is correct you can actually see strain in the tiller. Look at Karpovitz idealized schemes.....or others....the bend and the strain are concentrated towards the handle. This is also why a d/r will do better than a straight limb....because you can move your bend closer towards the handle without overstraining weaker materials like wood.
Why it is better to have the bend closer to the grip still is an enigma to me - I just know it will make your bow faster as long as you keep your outers narrow and as light as possible. We of course also have that string angle thing.....the closer your bend is to the handle, the better your string angle at fd...but tbh, I never really understood the effects of string angle....I have discussed that topic with more than one physiscian but never got a reasonable answer - please enlight me

I'm also adding a picture of my fastest bows, which are a horn/sinew composites. And one of a horn bamboo longbow which is very similar to your model 3 (although very slim compared to your model. If my bows were evenly strained the wouldn't usually all fail in that same spot

and btw Arvin: I think its true that the shorter bows outperform the longer ones with light arrows (due to shorter limb travel and higher dryfire speeds). On the opposite I dont think the longer bows have a advantage with heavier arrows at the same drawlength....that is a myth imho. These short reflexed bows can handle 10gpp very well.