The 80 gsm/10mm XPS skin will deflect a lot compared to 2 sided composite sandwich skins unless the ribs underneath are really close together.Remember in the monolithic foam thread where I mentioned varying skin thickness? If you layup root/tip/Dtube in a heavier, then finish with a single ply of <100gsm over top pf all. 80gsm/10mm XPS backing is enough to require not-accidental force to push through a surface.
And, from all I've heard, 80mm over soft XPS will get a lot of dings compared to more substantial layups over stiffer foam.
Part of the problem, I think, is some apples-to-oranges comparisons. Sure, a really light composite skin on XPS is less damage tolerant than a heavier composite skin, or one with a stiff PVC foam core, or aluminum. But, is it less tolerant to bumps than a fabric skin? Does it deflect less than a fabric skin at the same rib spacing? Folks seem to accept the fragilty and special handling rqmts of rag and tube without complaint.
The impact tests may provide some useful information.