You can easily search SCN and SAP notes to find that in case when output needs to be distributed to multiple emails the Contact Person functionality is the way to go. However, if "the client" is happy with whatever they have, there might not be a reason to rock the boat right now because in just a few years they might be facing the decision on moving to S/4HANA or another ERP. And they might have to make changes at that point anyway.
As I've heard, there will be some changes in the output functionality in S/4HANA (well, there better be because what we have right now is so 1999). Also there are some enhancements possible even in ECC 6.0, see the SD customer connection project: POST data