This isn't correct. AVX512 provides both a bunch of extra instructions, zmm (512 bit) registers, and an extra 16 (for a total of 32) vector registers. The donwnclocking only happens if you use 512 bit registers (not just avx512 instructions). The difference here matters a bunch since there are a bunch of really useful instructions (e.g. 64 bit integer multiply) that are added by avx512 that are pure upside.

Also none of this is an issue on Zen4 or Zen5 since they use much more sensible downlclocking where it will only downclock if you've used enough instructions in a row for it to start spiking power/temp.