Staying on top of updates is one of the most effective ways to keep your stuff secure and really should be done regardless of your setup. Updates have the downside of sometimes causing systems and applications to break. I think the question is what frequency do you want to update your applications.
I have been very happy with FCOS and really view it as building a declarative appliance. You can install it straight from an iso and configure it manually similar to Debian. But I really like the butane / ignition method for defining everything about it. Sort of like a more robust cloud init on the Debian side. I typically define this in a terraform openTofu project and then transpile it to my hypervisor as a vm so I can just keep fine tuning my config until I have it just right. I set weekly auto updates typically and for the most part rarely touch FCOS vms once they are working.