I was a head lifeguard for a handful of years in a big summer camp.
I have jumped in twice to save someone. Once was a distressed swimmer, other time was an active drowning.
One of the times was during a deep water test, the other time was when a kid was pushed in.
I do agree that good lifeguards job is prevention, and hopefully should not have to come onto saving anyone.
But, there is no way to claim - that you are a great lifeguard cuz you never needed to jump in.