I will have to wait and see.
But if the AMDs new lower CPU could beat the 3090 in the tests.
I would imagine that AMD would have used it.
You perhaps need to check what a CPU does and what a GPU does.
They aren't particularly related.
All the Ryzen 5xxx series has the extra SAM thing it's a Ryzen 5xxx series feature.
The (e.g) 5600X + 6900XT will be a fair fight/marginal winner vs 5600X + 3090.
The (e.g) 5900X + 6900XT will of course be faster, that's that the bigger CPU brings to the table. The GPU side of the score is the GPU's input.
An Intel chip + 6900XT vs an Intel chip + 3090 will be a MUCH closer fight and might even go to the 3090 by a nose. But then you've paid £700 more for an overall worse performing system as the Ryzen CPU is better.
The 6900XT will straight equal or narrowly lose to the 3090 regardless of SAM or not (OUTSIDE RT and without DLSS, sure, just to avoid being jumped on by a pedant somewhere. Even this is still in some doubt as there's plenty of tech coming online from microsoft/etc that'll give something like DLSS on the AMD cards too and their RT performance isn't utterly terrible either).
Pairing it with a Ryzen 5xxx chip will see it creep ahead (probably).