Reports that DDR5 stability is still a problem with Intel and other manufacturers. This adds credence to the studio projection that DDR5 systems may not surface until 2021 as development may take some additional time. A report from Bilibili in China suggested more work is needed to get DDR5 ready for action.
Intel LGA1700 12th Gen Alder lake ES3 is still not stable. 13th Gen Meteor Lake is also hitting snags. It is possible that the early run of DDR5 are not great quality but Alder Lake with its disparate cores may have to be altered.
Speculation that a new version of the Phi might come to market with HBM to improve throughput.
DDR5 is not likely the problem, it’s more likely that timing tables need to be refined as typical for the sector. Been a long time since zero wait state RAM was available,.