I can also imagine that you're not a fan of the buildings proposed by the Planet Zoo developers, because they're in the exact same style as what Pairi Daiza offers.
Not at all those building pieces were used as a demonstration in the DLC videos. I wouldn't use them in that way; they are meant to add decorative touches to your zoo rather than "build your own ethnographic village." I mean certain players like that kind of thing, but most zoo nerds wouldn't and think if it's not used in a utilitarian way for the zoo, it shouldn't exist. But I am grateful for the diversity of the scenery pieces because it unlocks many possibilities. Only these shouldn't ALL be used at once otherwise you aren't building a zoo.
As for the upkeep of the buildings, perhaps you know that the park was built around the ruins of an old monastery, hence the condition of some of the buildings. These ruins were totally forgotten before the park was built, and it's thanks to the it that they've been brought back to the forefront of Belgian heritage. Sadly, the ruins have become a secondary, even tertiary, feature of the park as it has grown in size. Initially, the idea was simply to create a ornithological park around the ruins.
Also, following the creation of a new entrance for the zoo, the area that corresponded to the old one has been undergoing work for over a year to turn it into a new small farm. The rest of the park (over 80% of the surface area) is extremely well maintained.
During COVID period, the Chinese section of the zoo was peeling paint from what I could remember and looked pretty shabby. Also, they are building yet another Japanese ethno-section despite already having their own mini-Forbidden City...
Finally, as far as the welfare of the animals is concerned, I can only rely on what I see and what I know about the zoo, as I don't work there. The park has been praised many times on this subject. It's certainly not the best in Europe, but it's far from bad in this area. Some enclosures could be optimized by being enlarged, but generally speaking, the space left to the animals is nice. From the 5 zoos I have seen in my life, Pairi Daiza is the best there.
Some of the animals look like they are crammed in artificial cultural buildings to be used as props and to signify "human ownership". For the visitor, trying to take photos it's not optimal. For the animals, they are probably bewildered why the place they are living in is pretty uncomfortable.
Why not use more natural looking rock instead?
White tiger in temple. Again, this is not a natural habitat for tigers so not ideal. Also, why is Pairi Daiza breeding already inbred white tigers? I hope for their sake they are crossing them out with brown tigers to introduce some much needed genetic diversity.
Another leopard in a temple.
Probably a better shot without the very distinct "Polynesian village" in the background.
Another "monkey temple"
Besides white tigers, I don't like the fact that elephants are still forced to give out rides and there are polar bear and walrus hotel rooms with direct underwater windows of polar bear and walrus pools. They can't swim without being watched 24/7. Same with brown bears who are terribly exposed with no caves so they can be watched 24/7 from hotel windows.
There's also so much wasted space. A mini-Forbidden City + fanciful recreation of a Chinese village, mini-Borobudur from Indonesia, mini-Angkor Wat, mini-Pagan from Burma, Polynesian village, African village, massive entrance that looks like the Vittorio Emanuele gallery from Milan, mock rice terraces, medieval Russian palaces, clearly the animals are competing for attention with the architecture in the minds of visitors which is not a good thing. Tiring and distracting to attention spans, it severely complicates the layout of the park, and increases the length of time visitors need to view the animals for no reason. If you are unfamiliar with the zoo, you don't know which buildings house important animals and which are mainly decorative. The cost of building such structures means higher admission prices and less money for conservation. If the park wants so much ethnographic stuff, they should just focus on doing that and not drag animals into it. Also, I need to remember that Pairi Daiza is a for-profit private zoo, so their choices make a lot of sense from that perspective.