Although I will agree that the Reefback should not be almost as large as the Dragon, the size of the creatures in the game are bigger than your POV. If you were to compare the character with the creatures, they are much bigger than they look from a …
Game director has explained why they won't be adding guns, and I would guess no turrets either. The weapons that don't kill have the highest chance of being implemented. Article: in Turrets and Base DefensesComment by dashingbronzeOctober 2016
I think the developers have planned one, because there is a "Sea emperor prison" or something. I've also heard that the Sea Dragon Leviathan and Emperor would "have a big role in the story." I think a story has already been planned.
I don't think Co-op will be coming out any time soon. I'm pretty sure one of the developers said that it would take them about 6 months to add a Co-op.