In order to maintain the feature class as a geometric network type when copying, that feature class would have to participate in a geometric network, so one would need to be built in the output geodatabase. I'm not sure of your end goal here, but it seems like quite a bit of work just to get some symbology applied to layer.
To answer your question about ...
As already posted in this answer, this now also works very nicely with sf:
fc <- sf::st_read("C:/path/to/your/filegeodatabase.gdb", layer = "some_featureclass")
But writing into a fgdb ist not implemented (yet?), you'd have to have a ArcGIS / ArcMap License as well as the R library arcgisbinding (see https://github.com/R-ArcGIS/r-bridge)