I think there are enough combat-capable ceratopsians (especially the ones with horns), but Jurassic World: Evolution 2 is missing the ceratopsians that have no horns.
While Microceratus is on high demand since its debut in the film Jurassic World: Dominion; I am not sure about Psittacosaurus and Protoceratops.
Here are My 4 favourits and the reason why i choose to suggest them:
1. Microceratus ( 1m long): Because of the screentime in JW Dominion it needs to be in JWE II sometime in the future.
2. Protoceratops ( 2,7m long): Scientiffic very imoprtant species that is famous for its "Nestings" and even one specimen that was burried alive while fighting with a Velociraptor!
3. Psittacosaurs ( 2m Long) : Scientiffic imoprtant species which fossils proofedd that some Ceratopsian had " protofeathers " looking like spikes on the back and tail along the spine

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4. Diabloceratops ( 3,5 Long): One Midsize Ceratopsian with a very unike Headshape and great sounding name for Show ..lol