You interrupt me during deep focus time[0] and the last thing you should feel is safe. There had better be a critical emergency, someone dying, major financial risk or otherwise an important+urgent issue. Urgency by itself won't protect you.
Otherwise you will find yourself the subject of this week's debrief meeting about "what didn't work" and more importantly, now responsible for paying for drinks and food for the rest of the team. We each have a block of time allocated and we aren't joking about how rare and precious actual uninterrupted time is.
[0] around 3 hours blocked out per day ahead of time.
An outage that can only be resolved using a single hero individual that must always be available to swoop in to save the day means there was no team backing them up. That seems less effective: It means no one is really taking leave. No one is taking real breaks. No one is doing real handovers either on a regular basis.
The "no real handovers" aspect means that the current state of each system isn't being checkpointed. We see that as a business risk. Not unlike what source code control protects against. Imagine you didn't commit code into git or similar for awhile. Still feel safe about rolling back changes? How are you going to roll changes back? Its a similar thing in people. If you don't do any handovers then stuff stays in one individual's head.
Your situation might be different. That's fine.