I decided to remove the new router completely and revert to my previous one. I re-enabled both WiFi bands and made the network names match identically to what I named them on the XR500. Everything that was previously online came back, including the cameras. This way I could also ensure if it were interference from another device on the network it would still exist. Needless to say it's been over 24 hours and none of my cameras have disconnected. I was getting upwards of 5-10 disconnects per day with the XR500.
I did the support call thing with Asus for the AC88U I purchased and the agent bricked my router within 10 minutes and I had to, on my own, use the flash recovery tool to bring it back to life. I decided to return the XR500 because I'm within my 30 days - I just don't have the time and patience to troubleshoot this. I know how these things go with manufacturers and support the majority of the time.
Maybe when Netgear sorts this issue out I will consider coming back, but this is way too big of flaw in basic functionality for me to look past.
Thanks for the help and suggestions!
I had withheld changing the network they were on because (if any of you are nest cameras owners you know this) I need to get my big ladder out and pop the cameras off to get to their barcode - a really annoying task considering where I've mounted these).