3.Arch is more than AUR. It's a bleeding edge, very lightweight distro. And both characteristics go into Manjaro - granted, there's a two week review period and some stuff installed on top. At the end, you get a super snappy, super nice system with a lot of value added on top of it.
I'm a Linux noob, using Manjo for almost two years no prob
One time an update needed manual intervention and I've fucked it up. But afaik on Arch this also happens so 🤷♂️