Notice that two Vega II are not 2x a single Vega II . There are giving about a $400 'credit' for swapping out the 580X module. The second one is "full price". Did a quick search of the accessories store. Vega II doesn't show up. but looks like the kit in a box version would be $2,600 .
Honestly don't have any idea why folks were trying to price anchor on the Radeon VII. This is higher than I thought though. Apple is really , really pushing for margins over volume here.
Not too surprising that they are scrambling to put perhaps "plain" W5700 cards into the BTO systems. The marketing ( real marketing .. user needs investigation and matching ... not the spin mastering) is whacked as it has been for the last 5-6 years.
P.S. [update... a bit of sticker shock so missed this too. The Duo is + $400 over linear on the Solo version. 2 * 2,400 4,800 wereas the swap-for-580X price for the Duo is $5,200 So another $400 in binning for dies that can sit relatively close together too. ]