That delamination is not a PU layer (like traditional packs where a PU coating is applied inside). Rather, it’s the film backing, which is 0.5mm RUV.
Anyways, clearly there is delamination there. That shouldn’t lead to any failure of the outer face fabric but it does make it stretch a bit more as the threads are more free to move around. There’s no reason to think different weight of this material (Ultra 200, 400, 800) would be more or less likely to do this, since the film and adhesive are the same, but there could be differences due to the film sticking better or worse to large vs smaller threads.
Two theories:
1) I wonder if a big factor in this occurring is that this is a frameless pack, where it looks like the back panel was quite wrinkled/scrunched. Notice how much wrinkling there is on the back panel. Perhaps as a result of that wrinkling over 1500 miles the film started to delaminate. A framed pack would hold the back panel tighter (a lot less wrinkling) and thus perhaps pose much less of a delamination challenge to the film.
2) Notice how the delamination is occurring where the wearers shoulders touch the pack. Since this pack is frameless, a fair bit of the weight could be sitting there and the fabric would be continually strained as the weight of the load is riding again constantly moving shoulders. So you have pressure and movement applied to the fabric. Then on top of that the Desert pack doesn’t have any sort of a backpad, so you have the pack contents pushing on the other side of the fabric which could be harder objects like a pot that add even more strain. My guess is that a framed pack would again fair much better for this reason (it loads most of the weight onto the hipbelt, rather than onto the fabric in the shoulder area).
Overall, for reasons #1 and #2 I expect a framed pack would fair much better.
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