But Superman traveled a lot more distance than Wally did.
Also Superman was dealing with pieces which were far more than billion in count. Moon has a mass of 80 quintillion tons, the pieces were a lot smaller than being 100 tons each.
One of the things that is absurdly good about the Moon feat is the sheer distance Superman needs to travel in order to rebuild the Moon. It's orders of magnitude bigger than your average city.
I used the volume of the Moon being 21.9 billion cubic km, or 21.9 thousand billion cubic m.
So assuming the Moon was smashed into cubes 1m in size, there would be 21.9 thousand billion of them. Some are larger, some are smaller, one could err on the conservative side and say they're all about a meter cubed.
So the time is about a billion times shorter for Flash, but Superman moved about 41 million times more 'items'.
So on those two values, overall, Flash is more impressive.
Distance I don't know, as JL #9 never gave one. Phildo mentioned he calculated it, and Superman travelled about twice the diameter of the moon? So about 7,000km. Haven't checked that, but it's Phildo, he wouldn't lowball this.
Flash made 266,000 trips (he saved 532,000 people, sometimes carrying one, sometimes 2; so I lowballed, and assumed he's always carrying two). He carried them 35 miles away, so that's a 70mile round trip, or 100km. So Flash travelled 26,600,000km.
Superman reassembled an inanimate mass -- huge, yes, but essentially a big rock, and it took him a few seconds. Assembling celestial bodies from bits and chunks is also in line with real processes (ie, gravity is gonna help).
Flash had to evacuate a whole city's worth of living beings, and he had to do it much more quickly and with much greater care (human fragility > rock fragility), over and over and over again. And there is no precedent in the real world for this type of event.
Flash wins, imo.
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Shinier than a speeding bullet.
When typing this you should've figured you were using some wonky math. I mean, if you count Flash making round trips in a tiny distance (35 miles) and you know Superman had to do round trips (to go and pick a different piece of the moon, get it back and fetch a different on) over a much bigger distance, you should already figure that the error of magnitude in 7000kms is flagrant.
Not only Superman did bigger trips, he also made a lot more of them (at least a billion by your own admission). Obviously he travelled a much bigger distance than Flash did.
I think that Flash still ends up being faster due to his feat being done in a very brief timeframe but the underselling of Kal's feat in this post is damn obvious.
But then you have to take the fact into account that the pieces were scattered across more than moon diameter and Superman had to go all over it to get them.