It is very nice that you took much time @Lianshen to explain and i understand that there is a super big difference. But a lot of zoos are not the special centres or the concrete parks but in between. And i understand that on the one hand it is important to show people and for education. But it is impossible to know if the animals are happy there or would prefer to be in the wild. ππ
Yes, often, there is a gradient/spectrum in how "zoos" are managed; I took some caricatural examples because it shows how zoos can be terrible or quite beneficial according to a given goal.
It is already difficult to tell if your neighbour or your family member is happy, so let's forget about such dream when it comes to others species. What you can do however is to do your best to offer the optimal conditions to captive individuals in a zoo; to take care of their welfare. That's where ethologist play a crucial role, in which they observe animals/individuals and, with caretakers or team of the zoo, make the enclosure the most confortable possible by rearranging the enclosure, providing adequate food, various activities etc., to make animals behave as natural as possible (like in the wild).
Sure enough though, there is a long way to go before most of the zoos get nearly as good as the top ones.