Yes, absolutely that is my understanding of immutability. It's why I asked the performance question, but Immer docs are convincing, I see your point.

Not a surprise to me that mwestrate is the author after seeing the description of Immer - he has an excellent graph knowledge and applies clever architectures & optimizations from that.

I recognize it's completely different from how MobX works, I simply mean to say that I feel MobX is superior and this mere idea of mutability / copying instead of smartly updating a graph and correspondingly only the observer portions of your UI seems like the core of that