F6F had more of an impact than the Corsair IMO. The 38 did more as well as far as I'm concerned, as one of them shot down the plane which carried their best tactician. But the 38 was just like the Hellcat: "Jack-of-all-trades and the master of none."
Don't forget the marines used f4u long before the hellcat came around. Pappy and his boys owned in Russell Islands-New Georgia and Bougainville-New Britain-New Ireland areas. The famous VMF-214 "black sheep".
I would argue that in Europe, no "plane" broke the Germans back... rather, the shier might and enormous numerical superiority of the Russians with the industrial support of the US broke the Germans back. The US's involvement was important but in no way was it at the same scale as the Russians. By the time the US air war over Germany was in force (~1943), the Germans already were in retreat on the Eastern front. Remember battle of Stalingrad was over and lost by Feb '43.
The losses the Russians took to push them back were staggering....
10,651,000 Russians lost
407,000 US lost
(thats not counting civilians).