You are looking at the scenes and assets from the gameplay trailer and assuming that they were all captured at the latest stages of development, when it's obvious they're all in different stages. It's a varied mix and some aspects clearly need more time in the oven than others. For example, Atreus' model in Ragnarok looks unpolished compared to the model in 2018.
On the flip side, the texture detail and lighting on the alligator like creature from the Ragnarok trailer is a generation ahead of the World Serpent model from GoW 2018.