How do you figure? I personally do not like, or trust, RM, just based on how often it breaks with updates as it is reported often in this forum. I would say that the main purpose of the hub is to process data sent from the devices and turn them into hub events (at the driver level), so that apps (like RM) that subscribe to the hub events can take actions on them. The hub also acts as a scheduler to allow us to run automations on set schedules. What app you use that subscribes to the device events to take actions on is the user's choice. RM is just one option.
Webcore, for example, is much more stable than RM. It has been around longer than the Hubitat Hub itself. It is no longer being poked at constantly like RM is, so it is quite reliable. If you don't like how RM gets poked at so much and breaks, just don't use it for automations that require dependability.
That said, I don't even use Webcore anymore, as I prefer app code for automations.
I do not use any hub security features, as I don't have security issues where I live. Still, using Hubitat for security is certainly better than using nothing at all. Just based on my convenience automations, which are many, that very rarely have any issues, I would put about 95% faith in it reporting for security issues, but if you feel that you need 100% reliability (is anything really 100% reliable?), you buy a dedicated home security system.
There is also a whole category of things that need dependability that are not security. I can tell you I have run my furnace totally from Hubitat for two winters now, using zigbee relays on the zone valves, and I have had no issues in two years. I can press one button to go back to local thermostat control should anything fail (hub or relays) but I just haven't had that happen.
Garden irrigation is another category that needs high dependability, and again, I have had no issues there. You can also say that you can't depend on leak sensors to detect leaks, but yes, may people rely on Hubitat to report leaks and turn off valves for this high dependability required function. The hub may not be 100% reliable, but it is up there, and it is OK to put a bit of faith in it for things that really need to not fail, even if there is a small chance it may.
How often does someone try to break into your house? That is the other issue, the hub has to fail just at the time when it is needed to be dependable, so the odds of it failing just before a break-in is even lower than the general dependability, odds wise.