I once wrote the powers that be a suggestion for a new fuel policy. I called it the Retrospective Fuel Policy. As far as I could see, it was the perfect policy, as it would cover all situations, whilst still actually carrying the minimum possible. It even saved a bit of wear and tear on the engines, as you could arrange for them to self shut-down as you approached the gate through fuel exhaustion. Strangely, I never got a reply.
All of the gibberish we get about fuel is always retrospective. When I order fuel I'm making a prediction. World of difference.
When the fly speck existed, it had a number of outcomes. First we all thought we had to win...and that was by carrying the most fuel. It was quite some time later that an FO told me that I had it the wrong way around.
And it was easily manipulated. One flight had an intermediate landing. For cost reasons we'd tanker fuel out of the departure point, to limit the loading in the middle. But, if you offloaded ALL of the tankered fuel, that gave you a negative fuel order for the fly spec, thus making you look good. And you then took the flight planned load out of the next spot, again scoring a zero, but actually loading expensive fuel.
Fly specs disappeared very quickly indeed.
Going back even further, there was a captain nicknamed 'Vapours'. He only ever carried the flight planned fuel. His diversion rate was so high that the company ultimately created a special adjustment just for him, giving him a extra 5,000 kgs on every sector.