The ISS isn't floating, it's in freefall. We've been doing rendezvous in freefall for half a century. Launching out of a deep gravity well at 0.9g means a rocket operating with a tremendous amount of thrust and a launch pad (or area) for the rocket to take off from. Making a precision landing through atmosphere from interplanetary cruise onto a floating platform is also very difficult. SpaceX has managed to achieve something similar but much less challenging and with much lower stakes and it requires a vessel that uses thousands of tonnes of concrete and steel.