There no difference in regards to vacuum vs pinch bonding when it comes to potential delam. They both accomplish the same thing and neither is more prone to it. Further, BOTH will delam if water gets inside. The big issue is keeping either from leaking by doing maint.
Also, I live in one of the dampest regions in the country and swear by my cover. It keeps the TT clean and dry and certainly does not "trap moisture" under it at all. That's because covers are designed to breath.
Not that it would make much difference though, before installing the cover I place a thick plastic tarp over the entire roof and down the sides about 2'.
Not only does the TT stay dry but after installing these covers I found that my Dry-Z-Airs only filled up once during the winter season rather than the three times they used to.