IMHO, IF the Hellcat FM is modeled correctly, meaning "historically correct", it will be a near even match with the Niki. When the Royal Navy did flight tests, the Hellcat gave the Spit V fits in the turns.
It was not the best in any one category, but it was good in all of them, in short, a well rounded aircraft capable of a multitude of tasks.
The Niki is helped in AH by the engines not being as unreliable as they were in RL. Read somewhere that their "in commission" rate was terrible, like only 25% of the planes were airworthy at any one time? Will find that text again and post it.
I agree with Kieren, seems that the Yank planes have been "downgraded" each time due to other pilots complaining about them.
American planes, especially the Jug, F4U, and F6F, were widely known to take a hell of a beating and still get their pilot home.
The Niki, in the hands of a "great" pilot, should give Hellcat pilots fits. But the average pilot in a Niki, if the FM's are even near correct, will be in deep toejam if he finds a Hellcat on him. A victory for the Niki in said situation would depend on the Hellcat guy screwing up badly.
But this is just my opinion.