This is an exhibit that I'd disagree with the inclusion of on this list. While certainly architecturally impressive, and if this list was ranking must-see zoo architecture, or must-see artwork in zoos, I'd absolutely see why this building would be a worthy inclusion. However, from the perspective of a zoo exhibit, this elephant exhibit simply seems... average. Personally, I wouldn't consider an exhibit must-see solely for its historical significance and architectural marvel, when the exhibit itself doesn't stand out in any which way. This building is no more of a must-see serving as an elephant house than it would be as a zoo's entrance or gift shop. I can think of a number of historically significant exhibits that are much more impressive, from an exhibitry perspective, and I'd be much more inclined to include a different historically significant exhibit instead of one that serves as a mediocre elephant habitat.
I think you are mixing up the terms enclosure and exhibit. While as an enclosure it might not hold up well to any modern standard, but as an exhibit this is a fantastic historical building. By your reasoning some of the greatest historical zoo architecture such as Budapest's elephant house and Antwerp's Egyptian temple should not feature on the Europe list. That would omit what in my opinion are two of the three most beautiful historical buildings in a European zoo (Berlin's antelope house being the third).