Because of Cera and her father I guess we have come to understand threehorns in general to be tougher, rougher, and somewhat more racist than other species. The best argument in favor of this view is Cera's LBT 5 statement about Threehorns being so bossy. But if we look at it objectively, I think we end up with Cera and her father being the only concrete cases of threehorns acting that way, while we never actually witness any other threehorn to do that. Tria is behaving completely different and so does Mr. Thicknose; Dinah, Dana, and Tricia are perhaps to young to be brought up in such a discussion, but I guess we can agree that they seem to be acting different from the way we saw Cera act just after her hatching in the original movie.
Longnecks, that would be Littlefoot, his mother, and his grandparents, but also Ali, her herd (old one included), Doc, Sue, Shorty, and Rhett (even with several more longneck characters not included I think it is obvious that there is a variety of characters here.
It may be safe enough to label spiketails as somewhat gluttonous judging from the very few we have seen, but there too is a variety of characteristics if we compare good natured Spike for example to the almost "threehornish

" leader of the Spiketail herd in LBT 8 / forbidden friendship.
For lack of anyone to compare them to we can
assume Ducky's kind to be gentle and good natured in general, but as we have none of her kind with a speaking role who is not part of her family there is hardly a way to make this more than an assumption.
And as for flyers, even within Petrie's family there is a variety of characteristics very notable in the sequels 7 and 12.
So my main point is to bring up the question if we have a really good point to link particular traits to a kind (rather than individuals) in general at all?
With several more references to this I guess some of the threehorn characteristics are more present than we see with the many "exceptions" in the movies, but other than that I think we would have a hard time basing characteristics ascriped to a species as a whole on facts presented in the movies.