I spent 19 years in the (respectively) Second Officer and First officer seat before I upgraded to Captain, I always took note of the Left seaters I wanted to emulate and, perhaps more importantly those I wanted to be nothing like.
A safe cockpit is one in which everyone is communicating with each other with no hesitation, this most certainly includes Flight Engineers.
As you know well Old Fella, the best Captains lead by example and almost never even have to mention their authority.
I don't know of any Boeing Or Airbus certified for single pilot operation.
All the very best Old Fella.