The FM-2 beat out the F6F by a CONSIDERABLE margin (think I saw somewhere estimated as high as 30-40:1).
Given that the Hellcat fought in greater numbers, there is no doubt it carried the greater weight in winning the war in the Pacific.
The F4F won the fighter war in the South Pacific. Guadalcanal was the meat grinder that broke the back of Japanese air power in the theater, and was to the cream of Japan's fighter pilots what Midway was to their carrier forces. Before Guadalcanal the Allies could STILL have lost the war. Guadalcanal guaranteed that they would WIN, and it was the WILDCAT that saw them through that campaign. Later fighters were really just the final nails in the coffin.
You have to examine the aircraft that were typically encountered by the FM-2. They flew from escort carriers, which meant that they spent the bulk of their time supporting ground ops, covering TBMs, and flying BARCAP for the CVEs. There weren't many fighters to be engaged. Mostly, they killed bombers and suicide aircraft. If you check the Navy Statistical Digest, you'll find this was the case. FM-2s never got anywhere near a big fight... The CVEs were too slow to sail with the fast carriers. Also consider that the statistical sample is very small. A dozen FM-2s on 15 CVEs doesn't add up to many aircraft. FM-2s did well, but the opposition wasn't especially deadly overall.
I would also argue that the F4F didn't break the back of Japanese air power. They held the door, but could not push out. There were many contributors to crushing Japanese air power. However, you have to separate the services. Wildcats rarely encountered the JAAF. They mostly dealt with the IJN. F4Fs were not very good as escorts, simply because they were hard pressed to defend themselves. I read somewhere that the the SBD killed more IJN pilots than the F4F. How so? It killed them while they were aboard their carriers. Nearly 20% of IJN carrier pilot casualties were the result of going down with their ships.
There can be no question that the F6F was responsible for the bulk of the devastation to Japanese air power. Hellcats shot down more Japanese aircraft than the F4F/FM, P-38, P-39, P-40, P-47 and P-51 combined. Over 5,000 kills.
My regards,
Widewing