Let's see, this is the actual chance calculation that we haven't touched:
https://github.com/TrinityCore/TrinityC ... m.cpp#L679
I don't know if it's the same as what Blizzard used, they haven't revealed everything.
For the change in team rating this compares your own team rating with the average MMR of the opponents. Your own MMR and the team rating of the opponent appear irrelevant so teams will get different results.
1754 - 1470 = 284
1553 - 1730 = -177
So even without calculating the actual chance, we can see that the winning team showed a higher rating difference in this example. And the higher that difference, the less their team rating will change. If they instead lost this match then they would also lose less than the other team would gain.
It might seem weird but this calculation avoids problems when a high MMR team creates a new team. Because of the high MMR, other teams won't lose much rating against them. But because of their low team rating, they will gain a lot of rating.