With 16 Gigabytes of RAM, the AMD graphics cards are attractive. But the Nvidia cards may have all the memory you need for the resolutions for which it is reasonable to use the video cards. As well, the 6900 XT, with the same 16 Gigs as the lower-end models, can't game at 8K, unlike the 3090, with 24 Gigs, which can. The AMD cards do create a quandary for Nvidia, even though its better software suite means they certainly can still get away with charging a modest premium.
This is despite the Nvidia cards selling out so quickly; eventually, they probably will have to add VRAM to remain competitive. But I don't think they need to improve their existing line-up quickly; adding cards at the low end, just as AMD presumably will do soon, is the priority. Or would be, if they can get enough silicon to meet demand; if not, they might as well use whatever silicon they have on the more profitable segments of the market.