While you might be right, as far as the walk thru aviaries is concern, and your point of cost efficiency is a sound one, I would also suggest to give them a little more time, it is a bit early to write them off? would you not agree? Just think about what we have been shown so far, while exceptional quality in all the models, an upgrade i would even say from Planet Coaster renderings, it is still just a small percentage of what the game will offer. The majority of the animals are still yet to be revealed, and the same could be said about foliage, architectural components, scenery and amenity items as well as game features. As example of this, i made a thread pointing out the very small variety of plant species in the African map game footage that Planet Zoo released, and Bo answered by telling us that much more was to come, and gave me an indication that foliage was very important to them, as to expect much more than what had already been revealed. Who is to say that with time many other components of the game currently unknown to us will appear.
Also I'm far from an expert in Planet Coaster, since i have not played that game, but by the looks of it, even after the base game was launched, there were an immense amount of items and packs added and made available for purchase. And again, with Planet Zoo we are not talking about a roller coaster, amusement park game, that dealt with an endless possibility of rides and themes, this is a zoo game, birds and aviaries are fundamental in the story, so they are a must. Only time will tell what happens, maybe one of the developers or Bo would fill us in this area, but i do think that there is definitely hope. And let us just say, that the walk thru aviaries are not possible right away, ok, what about just aviaries and mesh exhibits that we can create piece by piece and let the animals do what they naturally would do, fly, leap, climb, jump, without this type of exhibits included, then i would agree that the game has a huge gap from reality.