Kong's gonna be hairless very early in the movie when all that hair gets burnt off of him. Particularly now that Godzilla can just radiate heat/radiation as well as breathe it. Hell, Rodan lives in a fucking volcano and is constantly on fire, how you gonna deal with that? Giant oven mitts??
Kong also needs to get a lot more durable, because he bled a lot in Skull Island. None of the monsters in KotM took the same level of damage that Kong did, except when someone like Godzilla was ripping heads off. If Godzilla got a bite on Kong's arm, let's say...he'd rip it right off. Even if they are equal in size.
Seriously though, how does anything live in fucking lava??