Good question, although I'd suggest that anyone's answer will always depend entirely on what their alternatives are.
I don't know where I saw this, but just recently, I saw clip of a woman asking another woman whether it was more important to "look nice" or "smell nice". I didn't see the response (I think my partner may have just been flipping through channels), but to me, it seemed obvious that the question is impossible to answer without knowing exactly how hideous or foul you might look or smell if you say it's less important. You have to compare specific examples to other specific examples. You have to compare margins. And even then, it's not always obvious.
The term "just", to me, is akin to "moral", in that it is basically meaningless and arbitrary unless you define it with respect to some other goal.
The wealth in the society you describe could certainly be more evenly distributed. But at what point should I say it is, in fact, "evenly distributed"? The answer to that is somewhat arbitrary, isn't it? And even the assumption that "evenness" is related to "just-ness" is also, at some level, arbitrary.
To me, the best definition of justice is that, once a community decides on it's rules and laws, that those rules and laws are carried out as they were agreed upon - i.e. that there is no corruption. Although of course "justice" by that definition might not be good for everyone. In other words, "justice" isn't necessarily "good" at all. Although, since I don't believe it's possible to define an absolute "morality", I also don't think it's possible for anything to be universally "good".
Even a world in which we prioritize "collaboration" won't be the best world for everyone. Some people, after all, thrive on antagonizing other people, and so a world that values collaborators and fights antagonists would not be friendly to, for instance, serial killers. But I think a society that values collaboration above all else is the society that we can expect people who want to collaborate to participate in - which, it's no coincidence, are the same type of people who are capable of having their opinions changed through the types of conversations I try to have on Medium.
