Two fans are only preferred when the radiator dimensions aren't close to square, or if there's a mechanical limitation which prevents using a single fan. In almost no case will two provide better coverage than one. Instead of hitting the keyboard, let your avitar take a pee and let's do the math together. Suppose you have an 18"x18" core, which is to say 324 sq in. Ignoring shrouds and mounts, if you cool that with an 18" fan, the covered area would be 254 sq inches. If you cool that with a pair of 9" fans, the covered area would be 127 sq inches. In reality, the numbers would be even less favorable, since there's no airflow through the hubs. Assuming a 4" flat motor, the hubs reduce coverage by 12.5 sq in for the single fan, and by 25 sq inches for the twin fans. So the twin fans would cover just 31% of the 324 sq in area, while the single fan covers 74%.

Suppose the core was 18x24, or 432 sq in. The single fan would still cover 254 sq in. But you could run dual 12's, which would cover 226 sq in. After adjusting for the hubs, the single fan still has an advantage of 56% to 46% coverage.

Total airflow would be comparable, as long as the motors were identical and the blades of similar design. But the airflow would be more concentrated with two fans. This may actually be a valid design objective, since most of the cooling happens on the inlet side. But that wasn't your argument.

In a puller configuration, if one fan of a pair becomes disabled, airflow through the core can actually reduce to zero, due to the working fan pulling air through the dead fan. In a simple pusher configuration, airflow is cut in half. In a Mercedes configuration, with a mechanical puller and an electrical pusher, one dead pusher fan of a pair will reduce airflow by more than half.