I work as a derivative quant/trader in EM (mostly fx swaps and such) and think that the broker-dealers I transact with provide value. Otherwise, obviously, I wouldn’t need them! This may be a little controversial, but in most cases, being paid means you provide value. And when this isn’t true, it almost always has to do with government regulation.

Anyways, while I don’t have any experience with MBSs, you were probably providing value even if you didn’t think so.