That's the problem with that reasoning right there. A 330mm2 N21 can't possibly compete with the 3080, can it now. You may flood the shelves with them from Day 1 but I , and others like me are simply not in the market for a product in that segment. I mean if AMD could magically pull this off, more power to them and I would gladly buy the product, but realistically speaking, they need a bigger die if they want to address that market segment the 3080 targets.
330mm^2 @ Renoir density (or GA100) is around 21B transistors which is just over a 2x increase from Navi 10 and will be plenty enough for 80CUs + 256 bit bus + 128 ROPS. It may need a few more than 21B for the cache but maybe I am over estimating how many transistors doubling the ROPS and CUs will take.
If we compare Navi10 to Navi14 a 66% increase in CUs and a 100% increase in ROPs, Memory Bus, Shader Engines, PCIe4 lanes used 60% more transistors. Saying that N21 is 21B transistors is probably a rather large overestimate since that is supposed to have 100% more CUs, ROPs, Shader Engines but it has no increase in Memory Bus or PCIe4 lanes. There is an unknown regarding the cache.
Still a 60% increase in transistors for N10 to N21 would be 16.5B which at Series X density would be 390mm^2.
8 Zen2 cores are around 2B transistors + L3 cache + non GPU hardware leaves at most 12B for the Series X GPU which is 56CUs with RT, 64ROPs, 320bit bus and 2 Shader Engines. There is no way I can see that N21 needs to be 500mm^2 to support the rumoured spec or to meet the 3080 performance level.
With a more realistic number of transistors it can be done for 400mm^2 or less @ Series X SoC density and at Renoir density it is a lot smaller still.
Like I have said all along the rumours do not mesh with each other and the biggest outlier is the die size. I think N21 will be 400mm^2 tops if the spec is 80CU, 128ROP, 256bit bus + cache and it could be in the mid 300's.