This is all very true. The level design of this game is on par with something a hobby dev could make in under two days (assuming they don't need to make any assets from scratch). With the right tools, you can make detailed terrains of very large sizes at a rapid pace, both in UE5 and in Unity.Also developing open world games feels like quite the feat when you don't know about game engines but I that started working on UE5 can tell you that is far easier to do than it seems. I'm not getting paid a cent and yet I'm starting to make a somewhat detailed open world. With enough time, knowledge and dedication you can make one. But frankly seeing BotN in this crude stage after all this time feels criminal.
It's actually faster to make open worlds than it is to make instanced maps.