Who told ya that??

CDNA is 64 wide per work item. And CDNA1 I believe was even 16 lanes executed over 4 clock ticks repeatedly (ie: minimum latency of all operations, even add or xor, was 4 clock ticks). It looks like CDNA3 might not do that anymore but that's still a lot of differences...

RDNA actually executes 32-at-a-time and per clock tick. It's a grossly different architecture.

That doesn't even get to Infinity Cache, 64-bit support, AI instructions, Raytracing, or any of the other differences....