The data and configuration files in the /home/ directories should be distribution agnostic, as it is related to applications rather than the OS. Some distributions might tweak their version of applications to use different folder names in
/home/rob for example, but you shouldn't need to do much more than a rename of the folder or a symlink to get it to match what the application expects.
So creating a user on arch that has ready access to the files and directories already present in the debian home directories should not be much of a problem.
The first thing you need to do is work out the UID of the debian user, and make sure this is the same on arch. The UID is the "real" user id, the one you login with is just a human representation of the uid. Lets say that your arch user is 'rob', and rob's home director is
$ ls -alnd /home/rob
drwxr-xr-x 94 1000 1000 12288 Jul 3 21:36 /home/rob
The uid and gid (group id) are the third and forth columns. So this folder is owned by uid 1000 and gid 1000. On the debian side, this would correspond to the username and groupname you are familiar with in the passwd:
$ grep 1000 /etc/passwd
$ grep 1000 /etc/group
So you can see the group name is also 'rob' in this case. This is a distribution choice - some will by default create users with a primary group of the same name, and some will create a
users group (often gid 100) and make this the primary. In terms of sorting this out, it doesn't matter too much, particularly if you are the sole user.
I can't remember what arch does, but I am going to assume it creates a
users group with gid 100.
So we just need to create a new user
rob, and point it at the folder, and make sure it is set up with the correct uid:
$ adduser --home /home/rob --uid 1000 --no-create-home --gid 100 rob
Or if you want to create a group for rob first, do this:
$ adduser --group --gid 1000 rob
$ adduser --home /home/rob --uid 1000 --no-create-home --gid 1000 rob
Now set the password for the rob account
$ passwd rob
And login, and it should have access just as it did on arch.