And if you'd need stability once, you could just set Archive on a specific day as package mirror on your cache server.
In my own anecdotal experience of running a hobby server on Arch for several years, I haven't experienced anything to make me think the distro is unsuitable for server work.
You'll just have your upgrade dance clustered into a single event once every N years, instead of spread over randomly, based on major releases of SW your server depends on.
I think we all use the software we choose to use in order to use the software we choose to use. When we build a cluster, it's often done in order to build a cluster.
Eg. if major postgresql update comes, you'll have to upgrade your DB cluster very soon. If major update to some program requires configuration changes, or if scripting language has deprecations that you've ignored for years, etc. you'll run into trouble, too.
I've been running a few Arch Linux servers for ~5 years and it's been quite pleasant. Being able to use the latest features in various programs or scripting languages is a very nice benefit.
Well… at least its what I’ve wish I could say.
Truth is I’m using manjaro (arch based) on a similar board and then one day after an upgrade they just decided to migrate from eth0 to the current naming scheme based on nic driver. Had to plug in a monitor and keyboard to fix the situation. Home stuff so its all good in my case.