

ARC is the in-memory cache used by ZFS. If it’s completely off the effect can be dramatic. Under no circumstances should a larger cache cause anything to get slower, ever. Even the raspi didn’t have memory that is that slow that this is a reasonable outcome. By default on most distros, ARC size is capped to 50% of physical system memory. Keep in mind it is a cache: if something else needs needs the RAM, it will be released.
As a concrete example: I was recently working on a server where a maintenance task that should take like 12hrs or so at the worst somehow took 2 weeks (!) and still wasn’t finished. That was ARC being disabled.
I kinda get it for immutable distros, where you can’t just install dependencies. But other than that the appeal is also very lost on me.