The Epyc devices are lower binnings though! That's exactly my point. They don't seem to have the 3.5+ GHz parts available in a reasonable quantity. When Intel was doing this with "1 GHz" Pentium 3's way back when, they got crucified for a paper launch.
Are you sure they're lower binnings, or just equally good chips being run more slowly for reduced power consumption? The power budget per core on Epyc is quite a bit lower.
The 3700X and 3800X, both of which have higher base frequencies than the 3950X and also use 8-core chiplets, have been in stock near continuously since launch.
