Volunteers are generally not the most knowledgeable individuals, and often get facts confused in my experience. On my visit I saw three active polar bears as well as an aardvark (which was sleeping) and really such sightings are probably circumstantial. You visited during one of the hottest parts of the year, even people don’t like to be outside at these temps.I didn't see the Polar Bear. The volunteer stationed there said that the Polar Bear is rarely seen. What use is a great exhibit if you never actually see the animal? Detroit has the same issue with the Aardvark exhibit.
And a great enclosure should be constructed whether the public can see it or not. Yes, seeing the animals is an integral part of the zoo-visiting experience. Zoos must not just cater to the visitors, but the animals themselves, and having large and enriching habitats is of course a fundamental part of that. Sure, the views of animals may not always be amazing - but as mentioned, it is conditional, and everyone has different experiences. It shouldn’t degrade your opinion of the zoo.