To answer your question on how BOTW runs on such a weak device:

It depends on the size of the world, the amount of assets you need to stream in and out, how you going to handle AI in unloaded scenes, the platforms you intend to ship to, the workflow that you want. Its fairly easy to do in Unity simply by using async scene streaming, the big problem is how to implement it for your game in particular. You need a lot of knowledge not only on how to build such a complex game but also how to do it in Unity in particular (every engine has its idiosyncrasies that you need to learn).Īt the very least you need to understand how to stream an open world dynamically and in a performant way.

But it is a pretty herculean effort if you don't know what you are doing.

A game such a BOTW is definitely doable in Unity.