Here is a complex dependency graphs built with no nesting and no "special" methods, only a combination of `then` and `all`

  function test(name1, name2) {
    let user1 = User.find(name1)
    let user2 = User.find(name2)
    let post1 = user1.then(u => Posts.getLast(u.id))
    let post2 = user2.then(u => Posts.getLast(u.id))
    let comparison = Promise.all([post1, post2])
      .then(([p1, p2]) => DiffService.compare(p1, p2))
    let email1 = Promise.all([user1, comparison])
      .then(([u1, c]) => Email.send(comparison.text(), u1.email))
    let email2 = Promise.all([user2, comparison])
      .then(([u2, c]) => Email.send(comparison.text() ,u2.email))
    return Promise.all([email1, email2])
  }