I am quadriparetic, so reliability is also very important to me. I have shifted most of my critical use cases to Apple HomeKit over the last year and a half. Everything runs locally except voice control with Alexa, but voice Control with Siri can still work via cellular if that’s available. The rules you can set up are simplistic compared to smartthings, there are many fewer Device choices, but the reliability is very good.
There are some other brand options as well depending on exactly what you want to accomplish.
Your Phillips hue bridge itself can run without the internet, so there are some options there.
I still use SmartThings for convenience stuff with complex logic, like getting a notification if the guestroom window has been left open, rain is expected, and the guest is away from the house. It’s great at that. But for turning the lights on every day at sunset or unlocking the door every time I get home, I need something with more reliability.
The community – created wiki has a list of devices that can work with both Homekit and SmartThings:
http://thingsthataresmart.wiki/index.php?title=Devices_that_Work_with_HomeKit_and_SmartThings
Also the following thread might be of interest: