But Scotty did replicate it on the Enterprise after both him and Kirk were beamed back over. Why else was Scotty manning the transporter station? Plus when he finally understood the issue on why he couldn't complete the equation, why would that stop him from replicating it again on his own?
My issue was not so much that it was possible or replicatable but that it was suggested as practical for normal use. No special equipment, no increased power consumption, a standard low spec shuttle transporter or even a portable unit, and a magical formula. The danger was portrayed as beaming inside a warp field, not the vast distances. Even the dog, which was lost during an experiment months before, returns alive and unharmed at the end of the movie, albeit in an outtake scene.
TNG was quite vague on the cons of subspace transportation, citing it as unsafe but never once showing any negative consequences. It used the same power source as a normal transporter. Subspace communications require subspace relays because the signals get weak or diffuse if the distance is too long (an anular confinement beam would require a source and a lot of energy to keep the information intact, quantum linked, or whatever it does). I think the network is about every 20 light years or so. Presumably this would apply to a subspace signal carrying a transportee just the same. This I could get behind, being similar in concept to a Stargate bridge but It wouldn't make much sense in Into Darkness, where the relays would have to traverse enemy territory where subspace signals would be monitored and detected. You could probably get away with it a few times, assuming your relay was mobile and cloaked but given that it would have to stay in range to be of any use, it would probably have a limited shelf life. You would also need a receiving platform or at least a device at the destination to avoid splatter.
More significantly, transporters can send cargo. Why would Kodos need to starve his population if he could have ordered provisions on sub-space deliveroo?
So it seems to me that this type of transportation has its place in canon but with serious limitations. It should only work from a designated station with sufficient power consumption. It relies on a subspace network vulnerable to sabotage. It requires allies to run a receiving pad or spies to set up a receiving pad in enemy territory. It requires strategies to prevent enemies detecting the signal and tracing it to source.
The way it was portrayed in ST09 was very sloppy. The Enterprise should have been closer to Delta Vega. In Into Darkness, they should have tracked the signal through sub-space system. How Khan evaded detection should have been an open question for enquiring Federation minds (even if we don't need to know the answer).