Nit: technically, all Javascript functions are lexically scoped. The fat arrow permanently binds the value of "this", which is sort of like modifying the scope, but again not technically because "this" is a special keyword and not a variable.
I'm still trying to understand the details here, but my impression is that ()=>{} isn't a shorthand for function(){}.bind(this). The latter creates two functions, one with an auto-bound "this" and another with a manually-bound "this". The former creates one function, skipping the step of auto-binding a new "this" to it. So it just sees the outer "this" via the normal scope chain (I think). The idea being that JS is doing fewer things in the background and makes functional programming a little easier on the CPU.