Going back to RT's original comparison Nakajima C6N vs. Martin Mariner
"Background for this comparison is that both planes, no matter how opposite they were in concept, had the main task: high-sea reconnoisater. And both fulfilled their task, both spotted the adversary fleet at the Marianas battle."
I don't believe that it is true that both these planes had the same main task.
The Mariner was a twin engined patrol bomber that could perform a wide range of tasks including patrol, offensive bombing/depth charging, search and rescue, transport, reconnaissance.
It was a big twin engined plane that could carry 4000lbs of offensive weapons and was fitted with up to 8 x 0.5 inch defensive weapons. It was slow , in WW2 a sea plane only with open sea capability. By comparison with the Catalina that it supplemented it was faster, had better open sea capability and was more expensive. In the Wiki section of the plane it lists six comparable sea plane types including the general purpose Kawanishi H6K and H8K.
The C6N by comparison was a dedicated single engined carrier/land based reconnaissance plane. It had a token rear gun but largely relied on it's speed and altitude performance for safety and had no capability for carrying offensive weapons. The Wiki reference to this plane only lists one comparable plane the Mitsubishi Ki-46 as only the Japanese gave priority to developing and operating specialist reconnaissance planes.
The two planes may have performed the same task in the Marianas but the difference was that for the Mariner it was performing only one of the many tasks of which it was capable whereas the C6N was doing exactly the single task that it was specifically designed for and for which it was incredibly suited.
In terms of the Dutch experience with the Mariner, it is a lot of plane to be lugged around by two R-2600 engines. The loaded weight is approximately 60% greater than the NA B-25 fitted with similar engines. I can't see the Mariner having much surplus power with two operating engines and being very difficult in engine out situations.