You're making stuff up.
Latency issues? You do realise IO is not now per die, it has its own separate IO die. Where would the latency come from on the 12 and 16 core? The 2x or 1x CPU die core talk to the same I/O die.
Though it won't necessarily be the case, logically the 3900X will be a higher bin. If it is, then that likely means that with the right cooling and / or power delivery, it will clock as high if not higher.
You know that a 2990WX will do 4.2Ghz all core on a run of the mill water loop and a mATX board? Despite the enormously larger power requirements and heat output than a 2700X, the bins mean a lot.
Ouch.
I'm not making anything up. I know jack. Lots of people talking about potential latency and oc headroom differences though. These seem to be the concerns/queries people have. Several videos I've watched suggest it's unclear on what criteria you would buy which chip on.
Again.. I've not made anything up. I've not stated anything as fact.