Why is ECS better than actual Unity Entity-Component pattern ?

I have trouble understanding why technically speaking ECS will have better performances than the actual Unity Entity-Component pattern. I know that it will use the new C# Job System but is this the only reason ?

@Shashimee, because, it is how ECS utilities memory. Rather than in typical OOP, where memory data is scattered all over the place, ECS packs data tightly in chunks. Which allows rapid access to what is needed. Just to give rough pictured idea, it is kind of, like storing 2D array in 1D array and referring to row and column by single index offset. While in 2D array you need 2 indexes for row and column. So you go data nicely serialized.