Man of Honour
I'm not sure, wouldn't they need a new / redesigned GPU die, I thought Navi 21 maxed out at 80 CUs?
But, I think a super overclocked RX 6900 XT could sell reasonably well if it managed to overtake the RTX 3090 in 90% of games, with RT off, if priced a bit lower. Overclocking the RX 6900 XT will get a bit more 'milage' because of the extra shader units (in terms of TFlops). Maybe upto 2600mhz will be possible on air.
To overtake the RTX 3080 TFlop count, it would need a massive overclock of 2900mhz! Probably only remotely possible when LN2 cooled.
Just compare the specs of the RTX 3080 and RTX 2080 TI. The RTX 3080 has around 24% better performance, and has 2x the shader units and over 2x the TFlop count (which increased clock rate boosts further).
That accounts for most of that boost, but the RTX 3080 also has 8 extra ROPs and a bit higher memory bandwidth, which I imagine helps a bit with 4K performance .
2x TFlops won't double the performance of a GPU as you pointed out. But, that doesn't mean AMD has the luxury of ignoring this factor (AMD didn't with RDNA 2, they more than doubled in from the RX 5700 XT to the 6800 XT). TFlop count matters more when combined with other factors.
So basically you are telling me your original point was flawed as there are other factors that count when determining the performance of a GPU.