It seems clear one had to previously have had the Marriott Bonv°y AmEx $95 version (or its SPG predecessor) to be eligible for the downgrade.

The question is whether they are still doing this.

Considering that the rationale is to prevent AmEx from poaching mid-level (Chase) cardholders, and preventing a back-door evasion of the agreed-upon price-level segmentation among the banks, my guess would be "Yes."

Chase will be actively on the lookout for shenanigans, so AmEx will likely insist that only former cardholders are eligible for the downgrade to the former product.