More than a bug is something that the game has, that I don't like at all, which is about the issue of the appearance of the different creatures and the probabilities that they have to appear.
I can get the whole appearence shtick. Ark seems like a game that was meant with Multiplayer in mind first, meaning that if they allowed the better dinosaurs to spawn at a high frequency that people would be grabbing them and it wouldn't really make it a challenge.
I will say though that it might be better if they have a sort of "timer" where Dinosaurs a certain distance away from players despawn allowing for other dinosaurs of other types to spawn in.