First off, I hope it is clear that I am talking long trends and not local ones. I thought this would be apparent with phrases like "just a thousand years." What I'm saying is that the vast majority of people on this planet have better access to food, clean water, medicine, housing, etc than our ancestors did. I mean we have AC and people a few hundred years ago had shade and fans. This does not mean that inequality does not exist, nor does it mean that we've made the world a great place and no longer need to improve. It doesn't even say how much further we need to go, just "things have gotten better for most people." If you read my comment that way I do not think it is deniable, but fact. Interpreting it conversely is frustrating because I clearly stated longer trends, not locality.
Second off, inequality can still exist in positive sum games. You can even have players which have gained negative utility. Positive sum just means that the total utility from all the players is positive. Doesn't say anything about exploitation, fairness, etc.
Third, I'd argue that part of the presumption of a zero sum game is a problem in capitalism. Since many people see "games" as "if I don't get x then that is equivalent to losing x". Or "if person has x then I can't have x". This is the "we both can't be wealthy" mentality or "you having more wealth than me means you're better than me" mentality. Given your comment I think you'd agree that these are destructive mentalities, but they stem from (among many other things) thinking of things as zero sum games. Not that we all can be winners.
That said, I do think systems can be exploited and there can be bad actors. But that's not really what we're talking about here is it?
I also want to be clear. When I say there is not a finite amount of wealth I am assuming time exists. At any given instance there is only a finite amount of wealth. As time progresses it either increases or decreases. I am saying that given a large enough time frame (which don't have to be that large) the trend is of increasing wealth/resources.