Your example is non-sensical. It has nothing to do with a comparison between static types vs dynamic types, it is only the usage of an awful JSON library in a not so nice language. In F# you even have Type Providers for JSON that give you auto-completion in the IDE:

    type Simple = JsonProvider<""" { "name":"John", "age":94 } """>
    let simple = Simple.Parse(""" { "name":"Tomas", "age":4 } """)
    simple.Age
    simple.Name

and most importantly you don't have nulls.