What's the appeal of Arch Linux over Gentoo?

Not a troll question, I'm really wondering it. I'm a long time user of linux (since 98 to be precise), started with slackware and distro-hoped a lot until settling with Debian (everything just works there). My second favorite was Gentoo.

I wasn't following much news on new Linux distributions as it was seeming to be mostly new slight modifications of Debian or Red Hat rebranded for a while until suddenly Arch linux appeared and seemed to be massively appreciated.

So I'm wondering : What's the appeal of Arch? It looks like a very manual process to install it and hard to maintain and I was thinking that Gentoo was the perfect answer for people interested in strong customization of their distribution (even more today with even faster CPU for compiling).

Can someone explain the appeal of Arch Linux as I don't really see it. The only thing I can think of is that it seems to use binary packages over compiling them yourself, but that's actually a flaw in my eyes (my biggest reproach to Debian is that you often need to install many dependencies you don't need for one package because of the compilation options they chose).