AMD 7900 XTX with Vulkan here as well, wasn't faster on my test either. Might be much different on Nvidia though.
I assume the limit for me is memory bandwith, as the 7900 XTX has the same bandwith as the 3090 from what I can gather and I already reached ~60 t/s with Unsloth. Those would fit with the numbers Byteshape has for their cards.
4090 and 5090 have much higher bandwith apparently, so on those cards you can probably get much more out of the kinds of performance improvements they are doing.
4090 isn't that much higher than the XTX (I also have the XTX), it's 1008GB/s (4090) vs 960GB/s for the XTX's.
The 5090 destroys both at 1792GB/s.
It's not really one thing with the nvidia cards best I can tell it's that they compounded incremental gains from software drivers, card kernels and optimization from been the primary choice (plus first mover advantage).
I didn't buy the XTX for AI purely gaming but it's a capable enough local card for running Qwen et al.