Was the radar display on bright or was it left at full dim by mistake, hence maybe the 160/320 nm pic didnt show any Wx returns.These questions are difficult to answer.
When i was a senior F/O , I thought that i knew the radar like the back of my hand, only to relearn how to use it on my own as a captain.
There is [ in my opinion] some hesitation in deviating for Wx in many F/Os that i have worked with, Does not mean it applies to all.