Why Firefly is better than M4A3/76?

I was really obsessed to see Firefly in the game, when it came I was puzzled - why it was better than 76mm gun from M4A3?
And in fact, it's not better. Firefly became famous, coz had a very good nick and there were nothing better than his gun, because all other gun were just absent.

Here's article No1: The Chieftain's Hatch: US Firefly Part 3
http://worldoftanks.com/en/news/21/The_Chieftains_Hatch_Firefly3/
So why does Firefly get all the glory and positive reputation as 'Best Sherman'?
I suggest that it’s for the simple reason that it was there, and in numbers. The real advantage that Firefly had was not that the tank was better, but it was that the British Army had decided to implement it in substantial numbers before the invasion of Normandy. A number of 76mm tanks were sitting in the UK during D-Day, and HVAP was not yet in production. American commanders simply did not think they particularly needed it. Why add extra ammunition to the logistical tail of the battalion? Why make a bunch of expensive HVAP ammo when the standard AP was good enough?
These assumptions that the Americans had were simply wrong. It was not the fault of the tank, or the people who had developed the tank and ammunition in time to partake in the Normandy invasion. It’s not to say that Firefly doesn’t deserve its reputation, but arguably it does not deserve it as being a better tank than the 76mm M4, and the US forces are equally arguably given an undeserved hit for not choosing the tank themselves, beyond the 81 they had converted. (Possibly as much due to political pressure as anything else).
These were policy decisions. Remember that the decision had been made to build nothing but 76mm tanks starting 6 months before D-Day, but was not shipped over quickly enough. HVAP could have been built in greater numbers earlier, but absent a perceived need, the ammunition was given a lower priority for the raw materials. 76mm was a great tank. It just was never given the same opportunity to prove it.

And here's article No2: US Firefly: 17-pounder vs 90mm vs 76mm
https://forums.spacebattles.com/threads/us-firefly-17-pounder-vs-90mm-vs-76mm.285284/

The Firefly was a lash-up, so a tank that isn't (M4 76) is going to be better in some operating respects.

The problem with these academic arguments, trotted out to demolish a myth that only exists in the minds of the un-informed, is fairly simple.

First, they have to acknowledge that they are theoretical, based on a  highly artificial criterion - was the Firefly 'the best' Sherman? Who cares? The British tank crews in Normandy recognised the WORTH IN COMBAT of their Fireflies. That's a better criterion, judged by people who were there, rather than people who were not.

Second, the conclusion that the 17 Pdr was no better than the 76 relies rely on the stated inaccuracy of the APDS round (to use the actual term used for SVAP), based mostly on tests done in 1943-44. There is also evidence that accuracy was if not solved, improved, over time. In Normandy the British infantry had similary accuracy issues with the new APDS ammo for their 6-Pdr towed AT guns, but these were resolved (according to an account from one of their crews).

It is probably quite true that the Sherman 76 was a perfectly good tank by 1944 standards, just as the 75mm version was by 1942-43 standards. Somewhat better armour would likely have been desirable by 1944. Even the 75mm Sherman was perfectly good at maybe 90% of the things that tanks had to do, and its HE capability was said to be preferred to the 76, possibly because the 76's flat trajectory resulted in a much longer 'beaten zone'.