On Ice Lake Xeon the penalty for using the AVX-512 features on a single core is -100MHz. If we pessimistically use the slowest part Intel sells, that is a 5% performance penalty (2% on their fastest parts). The speedup from this work is 40-60% compared to AVX2. So you'd be a fool to take the side of the folk myth. AVX-512 works.

By the way the performance penalty for using AVX-512 on multiple cores when the multiple cores were already active is zero. There is no penalty in most server scenarios.