SASless: I share your dismay at the lack of a well deck. (What, LCAC's not available to move ship to shore? ???)
That said, I don't think the Marines have posited the airwing as being solely V-22. You'd expect a MAW to deploy with Heavy Lift (53's) and Med lift (22's) and the usual Light Attack (hueys and snakes) elements.
That leaves the concerns in re moving heavy stuff via V-22 answered ... but it doesn't answer the mail on how you move the typical load out of trucks and such ship to shore.
Doing it all by sling load under a 53???
Seems a bit confusing. I'd need to understand the requirements document that went into the LHA-6 (sample) to grasp why the folks at Henderson Hall chose to go that way. (Once again the Navy seems to be building ships for specialty reasons, not the multi purpose platforms ... see also that littoral combat DD thingy ...)
Put another way, why not just build more LHD's rather than a stripped down LHA? Cheaper?