ALL certified aircraft are designed to a 1.5X safety factor. So all Normal Category aircraft are designed to withstand at least 5.7G, and all Utility Category to 6.6G, and Aerobatic to 9G.
And yes, especially older aircraft are much stronger (and yes heavier) that required.
When the air combat place had a wing spar failure in a T-34 (Bonanza/Debonair wing), the aircraft was pulling about 12G while rolling. A modern finite model analysis of the T-34 showed it would have survived this, is there were not some fatigue cracking to start the failure. As a reference, the F-15 has a rolling G limit of 2.5G.
When rolling, the upgoing wing has a MUCH higher load that the average load on the aircraft.
Yes, when you start playing with lightest weight, you design to the minimum strength and weight to accomplish the task. Colin Chapman of Lotus was the king of light weight. Without the computer modeling, he made each part lighter and lighter, until it broke too soon, and the backed up one or two iterations. He was quoted as staying, a perfect design of a race car is one that completes the race, then falls apart on the cool down lap.