Such a thing doesn't exist. In this case, it's not objective because:
By definition, whether a game is good or not can't be objective. Opinion is subjective, and is also the only criterion to determine whether a pack is "good" or not.
Not really. Every pack gets a "huge amount of love" when it's announced and after release, because it's new and flashy and moves stagnant water. All it tells us is that people wanted something new regardless of what it is.
Of course there are objective measurements if games are good or bad, for example the malayan tapir is pbjectivly a cheap reskin.
Every animal in the game can be rated on an objective scale mostly based on distinctness, how common they are in zoos and what roles they can fill in what places.
Ofcourse its subjective how much anyone actually likes it, but for example the eurasian lynx was objectivly a better inclusion over the iberian, as its much more wide spread in both range and how common they are in zoos, making them much more generally usefull then the very specific iberian lynx, which whould have been more usefull to have for a few people, but a clear minority of the player base.
On the same basis a bird would objectivly be better then a bear for example, as we have 5/8 bears + an extra brown bear, but just one more bird in general, making the need for birds much higher for a complete and round game experience.
Sure people can still like the missing bears better, but statistics and the goal of this game to offer a rather complete zoo building experience makes more birds nessecary, same for south american and oceanian animals.
In the same vein the twillight pack offerd 5 iconic animals that brought something new and unique to their ranges and biomes, while being unique from other animals in the game.
Where 3/5 animals being carnivorans a bit much? Yes, but in isolation all of them are a great addition and now that they are in the game it doesnt matter that they came in a bundle. All 5 animals enhance the game immensly and finally after 3 years small temperate low budget zoos have enough animals to choose from to have an 8 animal zoo that looks different from other 8 animal zoos of the same theme.
And thats a great thing imo, cause remember, NA and europe were just as neglected as australia and south america where and especally european areas are finally more then literally just 5 animals + make believe brownbears and beavers or arctic animals.
