I've ditched all ARP, mDNS in my setup. Everything is static IP addresses: it vastly improved robustness against network glitches, which absolutely will happen to you.
If my router is unplugged or offline, everything with power can still communicate for example.
Nearly everything is static on mine too. I keep track of all the various devices' MAC addresses and assign them one IP. I also make sure that, even should I reinstall an OS on a device and "forget" to assign it a static IP, my router always assigns that MAC address the static IP I picked for that MAC address. I then keep a little range of IP addresses for unknown devices that the router is allowed to use when a new device shows up. Once in a while I log into my router and look which new device(s) I forgot to assign a static IP too.
When you say you ditched all ARP, did you do anything special? For example do you configure, on all your machines, static ARP entries for each MAC address of all your devices?
If my router is unplugged or offline, everything with power can still communicate for example.