You're still grossly overestimating the area required for AVX-512. For example, on AMD Zen4, the entire FPU has been estimated as 25% of the core+L2 area, and that's including AVX-512. If you look at the extra area required for AVX-512 vs 256-bit AVX2, as a fraction of total die area including L3 cache and interconnect between cores, it's definitely not going to be a double digit percentage.