Like many others, I agree they are the best ever in their respective venues. Snooker is basically one game with both offense and defense mixed together. ROS is the GOAT on these tables. The other cues games, from rotation, banks, one pocket, you-name-it have various nuances within themselves. If he so desired, I think Efren could master any particular game he wanted, and be the GOAT in that arena. I also believe to reach that level of expertise, you have to be totally in tune with the equipment. However, in each sport, the equipment reacts a little different. Size, weight, and cues all cause different results between snooker and pool. I believe that is why it so hard for any one professional to have success crossing over the sports. ( I think Allison Fisher has done the best ) I'm not saying they can't play the game, but it's these little nuances that prevent them from mastering both pool and snooker.
As stated earlier, Efren is a Magician (with a capital M) and Ronnie is a Genius with Talent.
I will add, Ronnie is the only player I can think of, that with the game on the line... and a crucial, difficult shot at stake... he thinks nothing of shooting left handed. With no hesitation on a 12' table.... That speaks for itself.