Unfortunately, that's the nature of the beast. The Mutant is an ultra-light minimalist pack with no frame, and comfort and capacity are the cost of such light weight.
It sounds like you really wanted a Variant 37 - a few more features, some aluminum in the frame to keep it stiff, and of course a few more ounces of weight. I have a Variant 52 and it borders on perfection.
By the way, the side pockets are not for storage - they are for holding the bottom of pickets and wands which are held in place by the compression straps.