The flaw in K’s logic is when he considers the earth to be the only “stationary” object in the universe, and when he measures the “speeds” of all objects relative only to the earth. This is a geocentric point of view, which Galileo did away with 500 years ago.

The moving rocket is moving not only relative to the earth but relative to everything else, and so we can't decide on the absolute atomic oscillation rates of the rocket and its passengers, based only on its motion speed relative to the earth, since, relative to some other objects, the rocket is not “moving” relatively at all. For example, if the rocket is moving away from the earth at 90% of the speed of light, in the direction of a galaxy that is ALSO moving away from the earth at 90% of the speed of light, then the rocket is NOT MOVING relative to the galaxy. Therefore, no one can’t say that the absolute atomic oscillation rates of the atoms in the rocket “slow down” a lot, due to the motion of the rocket relative to the earth, but not at all, due to the motion of the rocket relative to the galaxy. There can be only one absolute oscillation rate of the atoms in the rocket.

The “speed limit” was invented by Lorentz, not Einstein, and it was related to the “resistance” to the motion of a mass put up by a field through which the mass was moving.

And then, of course, there are the earth-relative “superluminal” galaxies, which are traveling at more than “c”, relative to the earth, and we are traveling at more than “c”, relative to them.