Feature class backup copy in SDE

I’m stuck with something I thought should be straightforward. I need to create backup copies of existing feature classes hosted within an SDE. Backup copies will need going into a Feature Dataset ‘ss’ that sits inside the same SDE hosting the feature classes. FC1 will have fields ‘Field1’, ‘Field2’ and ‘Field3’, and FC2 will have fields ‘Field4’, ‘Field5’ and ‘Field6’. I can do this easy if I read and write these two feature classes as Individual Feature Types, however I was hoping for a more elegant way to do this with Single Merger Feature Types and a Dynamic Writer that would fan out the individual feature classes honouring their schemas. When I try this second approach, resulting FC1 backup copy will have its fields ‘Field1’, ‘Field2’ and ‘Field3’, but also ‘Field4’, ‘Field5’ and ‘Field6’ that have been transferred from FC2’s schema. Same goes for FC2 which will also have FC1’s fields on it. What am I doing wrong?