Leatherback is a non-factor. He weighs 2,900 tons and is 267 feet tall. Godzilla weighs nearly 100,000 tons and is almost 400 feet tall. That's like having an anorexic child trying to fight the heavyweight champion of the world.
And we've seen how energy/plasma weapons hurt Kaiju. A single breath attack would seriously injure Leatherback if it didn't kill him outright. But Godzilla could put him down with a combo too.
Kong is the only real threat, and even then without the axe, he'll be playing keep away until Godzilla inevitably beats him down yet again.