The Leopard 2 was designed in the 70s. So for battlefield vehicle designs, that is not necessarily outdated. Most fighter aircraft in use today were desgigned in the 70s: Su-27, MiG-29, sure, we think they’re old, but the F-16, F-15, F/A-18 are roughly the same age.
That’s kind of the point of the article, I guess. What is a museum piece doing on the battlefield?