That is a hard question to answer. First the process for getting rosin may vary from place to place. Secondly, the quality of Rick Simpson Oil also is highly variable as well.
Rosin is basically referring to heat and pressure extraction that squeezes sap from the original plant. The big news about rosin is that it is done without solvents so the potency can be very high and yield a flavorful product. Think of wax that people dab. People also like it because you can easily make it from home unlike some other extracts. The level of THC can be 80% or more if done well, it is essentially a concentrate.
RSO refers to Rick Simpson OIl, which has its claim to fame as an oil that was originally made by a man named Rick Simpson who after ‘curing’ is own skin cancer gave the oil to other people who were ill and the legend spread.
To make RSO the cannabis is soaked in pure naphtha or isopropyl alcohol, and the theory is all the good compounds come out and create a thick tar like substance. Many people attempt to make their own RSO and some businesses now sell it as well. You will read many, many accounts online about this oil, but it is hard to say what is true and what is not.
The best way to know what you are getting is to take the two products to a lab and test them. As extraction varies wildly, the actual plant matter and so on, it is hard to say what effects one or the other may have.
I am not a doctor. This answer represents my opinion based on my experience and research only. I hope this helps!