The rust problem was a common problem for different car manufacturers. The Golf 1 has also rust problems for example. The reason is that the production volume of stainless steel / galvanized steel was too low in that aera. And for example Krupp steel prefer to sell their material to the local manufacturers.
The Golf 2 was better because they filled all cavity totally with body-cavity sealing.
The most problematic Alfa was the Alfa Sud.
From wikipedia (https://en.wikipedia.org/wiki/Alfa_Romeo_Alfasud):
Despite their sophisticated engineering, Alfasuds (especially the early ones) had a bad reputation for suffering from rust, mostly due to the poor quality Russian steel used in their construction, and the storage conditions of the steel. Worse yet, bare completed bodies had to be moved outside the factory after assembly before being taken to the paint shop in a separate building, no matter what the weather happened to be.
Since the (156 / 147 etc) models rust is rather uncommon (or at least on par with other manufacturers). My daily driver 147 has 264tkm and is 12 years old. Besides some surface rust on some underfloor parts it is perfect. I don't think I will do any rust repairs before the car gets stomped. The engine I have is known for doing 500tkm without issues but I probably stop at around 300tkm.
Here a video how they do produce today