I'm talking about a different use case where inference via assignment does not work, e.g. a method declaration:

    public List<Set<Pair<Foo, ? extends Bar>>> combine(
      List<Set<Pair<Foo, ? extends Bar>>> a,
      List<Set<Pair<Foo, ? extends Bar>>> b
    ) {...}

    type Quux = List<Set<Pair<Foo, ? extends Bar>>>;

    public Quux combine(Quux a, Quux b) {...}