Wow, you went full in on the TRÅDFRI/Xiaomi combo. Most Xiaomi sensors eventually fell off my network too. What seemed like a sure thing in the beginning turned out to be a royal PIA for me too. I know some owners like @gavincampbell had good success in the beginning, but I have not read anything about how it’s going for him now.
The TRÅDFRI falling off hasn’t happened, but I only run two outlets and one TRÅDFRI repeater, so that’s hardly a comparison. I have an Xbee, but I only plug it in when I need to check routing.
I ended up moving all but three of my Xiaomi sensors to an Aqara HomeKit Gateway and I sync them to HE virtual switches via Homebridge. I just learned about Mi Connector from @Royski, but it requires the original non-HomeKit version of the Mijia Gateway.
The Aqara HomeKit gateway works fine for me. I live in an old house, less than half the size of yours though. The Xiaomi devices are all end device to controller. I’ve heard that they do route through Xiaomi outlets, but it sounds like you’ve paid your dues in outlets.
If you wanted to throw another $60 or so at the issue with a Mijia Gateway and Mi Connector, that doesn’t seem unreasonable given your investment in Xiaomi to this point see edit below, but I’d caution you about throwing much more than that at the problem. Once they are on their own Gateway, the Xiaomi devices are very reliable and don’t drop, but that’s my experience in a small home. That needs to be kept in mind when discussing the viability of this.
I’m getting good results, but growing more cautious about recommending anything that’s not on the compatible devices list.
Sorry to be that guy - Caveat Emptor 
[Edit] Just re-read your post and saw that you’re using @tonesto7 ‘s version of Homebridge for HE. That would be the reason you’re not seeing very fast response from the Aqara Gateway. I’m getting almost instant response from mine using @dan.t ‘s MakerAPI version of the Homebridge app for HE. @tonesto7 is also recommending that HE users switch to Dan’s version. For Hubitat, it just works better.
