Not to be harsh or anything, just interest and curious, why Segisaurus and Metriacanthosaurus? Those aren't even found complete in the real world and they were just little words on old posters?
Ontopic:
Hard question, not counting the obvious ones (like Therizinosaurus)
Styracosaurus / Kentrosaurus / Cryolophosaurus / Tapejara / Gigantoraptor
Segisaurus was in that old Jurassic Park brochure making it in some regards the last canon JP species JWE2 lacked until its eventual inclusion. I also think it fits a nice size bracket just between Coelophysis and Compy. Overall I also like what Frontier did with the model of the creature.
Insofar as Metria is concerned, have you seen it with its pattern? It really took off when its design was lifted straight from some promotional artwork used for Jurassic World, the website or something other. The famed paleoartist Julius T. Csotonyi was responsible for this design and Frontier based the in-game model from it. Besides that, Metria was one of the embryos that Nedry stole from Jurassic Park. To move things further along when Jurassic World Evolution was announced it was one of the most striking animals in the trailer.
Personally, Metriacanthosaurus is my favorite medium-sized carnivore in the game and I feel its loss would be devastating. It helps that Frontier also has a soft spot for UK species, so I feel confident Metria will stay because it has a lot of indirect relevance to the franchise and has its taken on an elevated status thanks to the JWE series. Similar to Segi, I'd also argue that Metria fits a niche size and has a unique aesthetic that adds a lot to its appeal and its skins/pattern are great and varied.
Finally, if we are talking about known complete skeletons then we have a pretty high bar where very few species would be in the game at all, most dinosaurs are only known from some fragments to begin with so I don't think that is fair to exclude Segi or Metria from the game on that basis.
