In short, I was wrong. It would have been more correct to say that Intel has offered a workstation part with AVX-512 continuously since Skylake.
The wx-24xx uses the same p-cores as alder lake, but with avx-521 enabled. Same for wx-34xx but with raptor lake's p-core.
The entry levels xeon are believed to be identical to Core ix, with the e-cores disabled and avx-512 enabled. The extra I/O and ECC support is done by the chipset.
In summary, they just went to support avx-512 only on xeon w.
This makes sense, since must be hard to schedule between cores with and w/o avx (the e-cores doesn't have avx).