More fuel only means extended holding and a greater choice of in-flight planned destination alternates. It may increase your chances of landing at your planned destination, only because you can hold for longer than those on "minimum fuel". Where the 'extra' safety comes from is a mystery, all the time we have control over where we point the aircraft and up to the minute information about airfield weather, it is not compromised.
Well said.
It matters not how much fuel you took if the delays are more than you can cope with. As long as you keep a eye on your options and don't allow yourself to commit to a "bad" one.
I fly to various corners of the world and often am happy with as little as five minutes contingency fuel. If something makes the destination unavailable, then I'll have to go somewhere else. Simples. A
commercial risk, certainly, but not a safety issue.
What really matters is not how much fuel you can fit in the tanks but what you plan and do when it's running low. Many years ago as a junior FO, I used to look up to captains who took lots of extra fuel all the time (because they could). In retrospect, I see a lot of it was a lack of skill and/or judgement plus fear of the unknown. Quite a few characters went to pieces as soon as any sort of airborne fuel decision was required.
To reiterate: you can take as much gas as you like; what sorts the professionals out from the amateurs is keeping the operation safe when it runs low, for whatever reason. From what I read about the RYR diversions, they had some holding fuel but it wasn't sufficient, so they diverted and told ATC that they didn't want further delay (I don't think they got to the stage of PAN or MAYDAY). To me that satisfies the safety aspect.