We're going into ship of Theseus territory here, but do you really know the extent to which they overhauled the engine? Because when I hear blocky terrain I think of LOD generation which all modern engines use to save processing power. Unreal engine itself is still the same propeitary engine based on C++, which similar to CE, has been overhauled over the years. Really what I see is you getting into the semantics of what makes a new engine without understanding the changes to the back end.