The AMD 6000 series is exciting for reasons other than just cost.
Having said that, there are some important considerations to take into account.
Though I personally would not purchase the flagship 6900XT (because it isn't the segment I typically 'play' in price-wise), it is good for those that do relative to RTX3090.
You still need to consider a few things though.....
If you are on a 400 series board with a current 3000 series CPU, you'll need at least a $500 additional investment to (5000 CPU and 500 series MB) to gain all the bells and whistles.
That price means you're then approach RTX3090 territory but it also includes a new CPU and MB...so still better.
6900XT works great from the standpoint of somebody who has nothing at present...wants the absolute high-end and is simply collecting parts to build a new PC.
The other, is if you are willing to sell your current generation pre-500/5000 parts to offset the cost of the new CPU and MB.
The RTX3090 is way overpriced for what it is compared to the RTX3080 performance.
In my mind, it only makes sense if you are a content creator...you need to 'feed' multiple high resolution monitors...or somebody else is paying for the card.
It'll be interesting to see what performance comparison relative to a new gen AMD system an RTX3090 paired with current gen AMD components could deliver.
The RTX3090 cost can only be justified against the 6900XT' if they are close without having to invest in a new CPU and MB to gain parity.