While we are also at it, without the SO or SOs the company would require another captain or FO like other airlines who are paid a fair bit more.
Yes, the CSM manages a team and that's fair enough, but can the CSM initiate an emergency descent? Handle an incruise engine shutdown? Or divert the aeroplane and land if the operating crew is incapacitated?
The SO can do all of those things. The SO could also easily do the CSMs job if called upon without to much bother.