The only other group that I see that I have that may be related is kvm so could try adding that too, I can see in the bash history for root user that I only modded my user to add that group but I’m also on Arch so YMMV. Looking at /dev/input everything is root:input except a few things which are root:plugdev but the two devices I pass are:
lrwxrwxrwx 1 root root 10 Feb 17 12:01 /dev/input/by-id/usb-Razer_Razer_Naga_Epic_Chroma-event-mouse -> ../event26
lrwxrwxrwx 1 root root 11 Feb 17 12:01 /dev/input/by-id/usb-Razer_Razer_BlackWidow_Ultimate-if01-event-kbd -> ../event257Which have ownership:
crw-rw---- 1 root input 13, 90 Feb 17 12:01 /dev/input/event26
crw-rw---- 1 root plugdev 13, 257 Feb 17 12:01 /dev/input/event257