Mount points are specific to one install - for example, you can mount your Manjaro root partition as /mnt/manjaro on Fedora. From every distro’s perspective, the partition it is installed on is /.
You seem to be mixing up the locations of partitions and mount points - a partition is somewhere on a disk and a mount point is basically a sign that points to it, and every distro can have different signs that point to the same thing.
You only need mount points in each distro for partitions that you want to be able to access from that distro. If you don’t need access to your Arch system files from Debian, don’t mount the Arch partition in Debian.
But if you have a partition that you want to access from multiple distros, you don’t need to use the same mountpoint in each distro - just like a USB flash drive can be E:\ on one Windows computer and H:\ on another - that is just a name and the files on it are the same.