no, it does not. just add more bits of entropy to your password if you want more "unguessability". there's no benefit to putting it into the username.
the username and password fields can be imagined as a single field; whether the entropy is at the start or end of the field makes no difference. we just split them up for database efficiency reasons. (and because the username ends up displayed some places.)
> I do not imply that password should not be complex etc.
I do understand that's not your implication
> I am merely pointing out the benefits of having a difficult to guess username.
i'm saying that if your password is good enough, it doesn't matter what your username is.
the same way that if the last 50% of your password is "good enough", it doesn't matter if you plaster the first 50% of it onto billboards.
Does that make sense? I do not imply that password should not be complex etc. I am merely pointing out the benefits of having a difficult to guess username.