Welcome to the forum! 
I am guessing that this was the intent somewhat, yes. But as you noted yourself, pamac covers more than just the Manjaro repositories, because it also offers access to the AUR, and it can be used for installing Snaps and FlatPaks.
I’m guessing that pamac was developed with the intent of broadening the scope of the package manager, given that Manjaro sought to attract more users — of the wrong kind, in my personal opinion, because Manjaro isn’t a suitable distribution for everyone, which is painfully manifest all over the forum. 
Oh, believe me, someone who shall not be named but who is one of the Manjaro leaders has once had the not-so-brilliant idea of omitting pacman, but luckily, the wiser people among the community were able to dissuade him from that horrible idea.
The facts are that Manjaro is an Arch derivative, that it closely follows Arch’s decisions, that pacman is the Arch-standard and virtually perfect — i.e. without bugs — package manager, and that pamac is (still) a buggy mess.
Many of us either never use pamac or only use it for installing packages from the AUR. It is always recommended to use pacman unless you want to install something that isn’t in the official Manjaro repositories.