120.4, wasn't that exactly what you were saying?
Why deviate for weather in a direction where you are sure there is other traffic, because ATC told you it is? Guess turning another way would be easier then.
Personally I think you can discuss this for ages, as it all comes down to pilots interpretation of how severe the weather is. I don't have the experience that 411A has, therefore I might be more cautious than he is.
A cumuliform cloud with tops at FL100 probably won't kill you, because it hasn't grown into full proportion yet.
As I said, traffic density and frequency congestion are factors in deciding wether to divert around it or not.
P77