Yes, I would totally agree that it is a different sense of justice from Amos. I read somewhere as I was prepping for the post that the wisdom literature, while not calling for the social justice of the prophets, that it did call for universal justice. That triggered Job for me and made sense, except that I wasn't using Job. However, I believe that I see the same challenging or questioning of justice in some regard with Ecc. 3 and 4.
As to why I would gravitate towards that more traditional view (though I was unaware that I was), I don't know. I like the challenging nature of it, the search for something. Those things intrigue me. Yet, I am troubled that its uncertainties are products of human experience with a loose divine authority (if that makes sense).