Well, I cannot read the explanation, but I take it the plane was designed as a "bomber destroyer", a class of aircraft the US abandoned prior to WW2. I suspect that plane was never built because it looks to be just at the end of the era of bomber destroyers.
The bomber destroyer was to be a heavily armed and armoured aircraft to intercept bombers, but not fight with their escorts (actually, the idea of escorting bombers was a later idea). Maneuverability was secondary, heavy guns the big thing, plus long range to intercept bombers way out there.