It is a bit (or not even a bit) off topic, but when you mean that you recreated (or formmated) the file sytems to be mounted at /, /home and /root, does that mean you realy have a separate file stem for /root? When that is the case, can you please explain why you choose for this uncommon behaviour.
IMHO the very existance of /root as root’s home directory, not inside /home, but inside the root file system was done to avoid it being in a separate file system that probably could not be mounted one misserable day in the future. In other words, when the mounting at boot of /home fails, the home directory of root will still be there when it is inside the root file system, making login as root still possible.
about your install, there seams to be some sort of confusion, you mention both / and /root, the /root folder is where the super users confilg files go, it shouldn’t be on a different partition (it can but that will only confuse things)
you really didn’t have to format /home as the applications that can use the old kde4 config files (like amarok) will continue to use them plasma 5 uses a different configuration scheme