I wish I could remember exactly where this was spelled out, but I seem to remember a couple of years ago they re-worked the matchmaker to mitigate against roster engineering. I specifically remember them saying that they would weight the top bases much more than the mid-level to bottom bases in the lineup.
Maybe someone else remembers when this change was rolled out. I'm guessing they probably started using (and hiding) offensive weight around the same time.
Hopefully I'm not imagining that.