Sorry about your bad luck with MLife but I don't think your issues really have anything to do with the relationship as such. The issues are the customer service (or lack thereof) when dealing with MGM/MLife.
Outside of the status match levels changing a couple years ago (between Hyatt and MLife) the rest remains the same in my experience. Maybe because I only go to Vegas every other year and therefore don't have a lot of data points but I've never found MLife status very rewarding so I just write it off as access to their "insider" discount hotel (and sometimes show) rates and free parking and don't really expect much more.
So in summary, outside of the general "decay" of MGM I don't see any issues with the relationship and its nice to get some points when staying in Vegas but that is not what motivates my choice of property when in there.