Yeah, the math has seemed broken on this from the beginning. It may have to do with the overall rating of the opposing team and your own team's rating. Like if you lose to a lower-rated team, you lose way more points, and beating a lower-rated team gets you very little. Most rating systems work that way. It just doesn't work AT ALL in something like Overwatch because A) the ratings mean dick in general as far as actual skill, and B) team ranking doesn't reflect in the least how well a team will work together (unless they're a group who actually plays together all the time; but of course most of us play mostly with randos).
Which is again why I sort of don't care. I think my high this season is 2,400, which is slightly up from where I started (like 2,300-something), but I don't really even keep track of wins/losses. When gpw and I compared our stats, they didn't even make sense. We mostly play together, not solo, and the number of matches it said we'd each played seemed way off.