That's a wing loading from the 70's. Nowadays it's considered a heavy plane (if we're talking up to .60 size aerobats).

Back in the 70's and 80's, planes were way over-built. They had thick plywood doublers from the firewall to the rear of the wing saddle, triangle stock on all four corners of the fuselage running nose to tail and basically no weight-saving measures. They were designed trying to survive impact.

We figured out that planes like that were more likely to impact the earth because they were heavy. And to make it worse, their weight made them more susceptible to damage due to more inertia.

Now we do everything we can to strip weight from the plane so it will fly as well as it can. Lighter planes are more aerobatic (respond faster and maneuver in a smaller area).

Point being that rule of thumb is out of date.