The Zero could turn and roll much faster and pull more G's than the Hellcat could at typical dogfighting speeds, that is a fact. And although roll rate dropped off at high speeds (this could be compensated for somewhat by using the rudder), the Zero's turn time remained easily quicker than the Hellcat's everywhere between stall speed and 450 km/h. That is why US pilots were instructed not to dogfight Zeros, which is also a fact. They even went as far as to put it in writing not to dogfight a Zero. All dogfights include high G maneuvers and bleeding off speed, it comes naturally when trying to out turn your enemy. And the faster the engagement's initial speed, the faster the rate at which the speed drops. If you're not pulling G's, then either you or your opponent aren't really trying. The definition of dogfighting is aircraft trying to outmaneuver each other at close range in order to find an advantageous angle from which to shoot the opponent. This type of turning dogfighting simply didn't take place at 500km/h in WW2. These aren't swept wing Jets we're talking about... in fact the F6F3 Hellcat could barely reach 502km/h at sea level while flying straight and level with maximum power. It's TAS at high altitude was obviously more, but the point is it took some work just to reach 500km/h in WW2. Also remember that any Zero pilot worth his salt won't be fooled into following you into sustained dives and maneuvers reaching very high speeds. He'll let the Hellcat pilot dive away and get him when he comes back up for more. Of course if the Zero pilot is inexperienced (which was mostly the case after 1942), he probably would make such a mistake.
When the trial between the captured Zero and the Hellcat concluded: “Do not dogfight with a Zero 52. Do not try to follow a loop or half-roll with a pull-through. When attacking, use your high speed performance to engage at the most favourable moment.” The conclusion was applicable to pilots of all experience levels (most US pilots were experienced and very well trained in any case). They evaluated the aircraft not the pilots, so the findings of the trials were applicable to the Hellcat vs Zero scenario. Nowhere did it say: Experienced pilots can disregard the tactics that keep you alive. In fact, it's following such tactics that make a pilot experienced and good. This is the difference between a good pilot and a "cowboy".
You almost make the Hellcat sound like it can defy the laws of physics. Sure, it had a top speed advantage. But the fact is it wasn't better at everything and it certainly wasn't better at dogfighting (even the USAAF acknowledged this). The Hellcat was heavy (2.5 times heavier than the Zero). It's power to weight ratio was worse than that of the Zero (477 hp/ton for the Hellcat vs 604 hp/ton for the A6M 52 Zero). The Hellcat's wing loading was much higher and its power to wing load was also worse. The Zero could also climb faster at low and medium altitudes.
If your opponent was a complete novice that barely had basic flight training and could barely hold his lunch down while flying straight and level (which I must admit was mostly the case for Japanese pilots after 1942), then you might talk about shooting fish in a barrel, yes. And the experienced Hellcat pilots made absolute mince out of inexperienced, hastily trained Japanese pilots. But if the Zero pilot knew what he was doing, not even the best attempts by a Hellcat would be successful. This was demonstrated when Sakai single handedly held off 15 Hellcats without being hit by a single bullet. The Hellcat pilots were experienced, well trained naval fighter pilots but they still couldn't hit him. The Zero was an aircraft that could shine in the hands of a good pilot, while a poor pilot wouldn't get very far in it.