Might be a hot take, but I find it kind of hilarious and hypocritical that there are a lot of people hating on the Black Rhino for just being another Rhino(3), but then get super excited about filling out the Ratites(5) and Bears(8)
As someone who really didn't like the rhino, here's my reasoning:
All of the in-game ratites look very distinct in size and appearance, and are from different continents and/or different biomes: Rhea from SA grasslands, Ostrich from the African deserts and savanna, Emu from basically all over Australia, cassowary from the tropical regions of Queensland and Papua New Guinea, and finally the Kiwi (which is the most unique of the bunch) being our only exclusive New Zealand animal and one of only two animals from NZ.
A similar thing can be said about bears: while eight bears is personally a lot, and some of these (notably Formosan, Sun and Sloth) share the same habitat and region, at least they look pretty distinct. The Sun Bear, for example, has short fur, a long tongue, and its trademark yellow chest patch; the Sloth Bear, which lives in a very similar area (with some overlapping even), has long shaggy fur which makes it stand out quite a lot. Formosan Black Bear... Well, it was in the base game, can't do much about it. Then we have the Himalayan Brown Bear (a baffling choice, I know, but at least it's different from the other Asian bears...?), the spectacled bear, which was heavily requested, and the iconic three: the panda, the grizzly and the polar bear, which are kinda essential for a zoo game.
As for the rhinos instead, well. Two rhinos are absolutely fine: one representative for Asia, and one for Africa. But two African rhinos? That's kinda overkill, especially when the two species look so close and are basically from the same habitat. Heck, they even had to make the black rhino darker (even darker than its real-life counterpart) to make it stand out