Nope, I believe you.
Those diesels have lower compression for the turbo's sake. Many non-turbo diesels have higher CRs. But that shouldn't be mistaken for an optimum CR for diesel, its just the CR that will make it operate without blowing the head bolts off
But, back to the topic at hand. I'm not sure why there would be a benefit to a richer mixture for less compression. I understand your demonstration about them being packed closer together with more CR, but the fact is that there are still only 14.67 liters of air required to combust one liter of gasoline. I wonder if the turbo crew makes wetter curves while not under boost to help smooth out idle or something. Often times they have to use such large injectors to supply enough fuel under boost that they're too large to idle at the proper delivery.
I've also heard that mixtures are most of the time purposely tuned richer under boost to help cool the combustion and give a safe barrier against detonation.