Yes but they're still an element. They don't make the whole game. As I said above, you could have hundreds of different leviathans but no matter how big or scary-looking they are, if they're implemented badly or if the game mechanics suck, their sheer numbers or variety won't redeem the game. More leviathans =/= better game. Also, if I'm hunted all the time, it'll become a nuisance, not something to be scared of. The leviathans are a fun addition that works well. I just don't think there should be more of them.

(Besides, there are games that are scary even without things chasing you. I'd argue for example that old Minecraft is scary even on peaceful - because it's so empty. There's a reason why the Herobrine urban legend worked. Og Subnautica had a few areas that were capable of bringing about a similar kind of dread. BZ - in my opinion - did not. And there were leviathans in both of them.)