We have a 4000 sq ft home with an at&t gigabit router connected to a deco mesh wi-fi system (3 routers). If I understand correctly, you do not recommend using a wi-fi mesh system with the surety security system. Would i need 2 alarm.com gateways for the security system? How would those be connected?
That networking advice is based on some popular early Mesh routers having very aggressive optimization features and almost nothing in the way of user configuration, which introduced some insurmountable device lan connectivity issues.
Most mesh routers do offer some configurability, and lately we see fewer reports of issues. The Deco Mesh wifi you mention I believe supports a connection preference setting to allow you to specify the network band a specific device connects across.
That is something you may be able to use to limit your panel, secondary keypads, and/or cameras to 2.4ghz to improve reliability.