I read that the jump by Kirk and McCoy would have severely injured them or killed them. They would have either landed into the rocks, or they would jumped into the equivalent of a liquid concrete. That is real world realism.
Do we know for sure gravity on Nibiru equals force enough to make a fall from that height lethal?
says Nibiru is class M (though I don't recall that being stated in the film,?) One aspect of a class M planet though...
The gravity on these worlds was Earth normal. The gravity might be slightly less or slightly more. (TOS: "The Cage"; TAS: "The Eye of the Beholder")