I do see your point, but I think some context about where I work helps here. It's a very chilled company and all teams are very self-organising. In the case of me needing to find cover, I would just drop a message in our on-call slack channel and someone will almost always pick it up (and do the necessary stuff like adding an override in the opsgenie rotation). If nobody happens to see it (unlikely) then I would just let the alerts escalate to the next person who would be happy to pick it up because they know that people don't let alerts escalate without a good reason. Everyone cares about their colleagues so they want to help if they can (it's also quite a small company).