The low-aspect ratio plane, like the Boeing 396, did not need to props counter-spinning over the wingtips. The Arup plane was what celled Zimmerman's concept for a VTOL twin-rotor craft; He worked for NACA and was on the team that saw the Arup S-2 fly and it made slow landings, and flew 97+kts on 37 horsepower. It did not exhibit any supposed detrimental excessive drag due to wing-tip vortices at cruise low "A" flight. It was sleek and quick, as an all-wing.
It was after that, when he won a context with a low-aspect-ratio twin-rotor hovering craft. His early patents show plainly that's what the twin props were for.
Look at the NASA Studies of the Wainfan Facetmobile. At low speed very high A flight, you want to huge wing-tip vortices, to keep the flow from the leading edge over the top of the wing from separating, to allow the low-speed flight. You wouldn't want to counter it if you could. As it turn out, The V-173 didn't. It still made the super-slow flight, despite the counter-props.
It seems to be a myth that all low-aspect ration planes suffer high drag due to those supposed vortices. They're not present at cruise.
The huge giggle-factor inducing props were an un-necessary complication, and the gearing system for them doomed the XF5U to being impossible.
If the Navy had contracted Boeing to build the 396, as an honest study of the Arup planform, things might have been different.,
A jet would have done fine.
Why the Navy accepted that the huge silly flappy twin props over the wing-tips were necessary, we can't know.
We might call the V-173 "Zimmerman's folly" or how the Navy threw away the Boeing low aspect-ratio fighter.