If you're fearless, you're dead. If you have fear but have the courage to stand against it, then, ok, maybe you can survive. But, no, the Rangers and Deltas weren't trained properly for the kind of warfare that acctually went on. They won because the Japs made a couple of major tactical blunders and didn't have the proper equipment to withstand the US onslaught.
I'm from this part of the world. Many of the big battles were fought around my country.
Ok. Maybe the Rangers, Marines, Deltas and whoever, Gurkhas, Shindits, etc, etc, etc, etc, etc. did have some Jungle ops. training, but those were mainly crash courses carried out before the actual assults.