I briefly considered Arch, a few years back that I was having a relationship crisis with my Fedora. Unfortunately it was a no-go for me for the following reasons, but the situation may have been improved since then: 1) Back then it was only recently that they had instituted package signing and verification for their official packages. Ouch! That was something that most distros had for years back then. So security was…
I think all of the 'other package managers' are just wrappers around pacman to give more functionality. I haven't seen any competing completely different package managers. Packaging, yeah, some stuff is only AUR, but that's generally a better starting point than "well here is the source". In general, 99% of what I use is available in proper packages. Obviously that'll depend on what you use.
Definitely not when it comes to security. We are talking about packages, which means even legit, well-intended programs can be weaponized by the packager.
That's a hell of an attack vector.