Yes, it is true that you will get an importance ranking. And, the higher your importance, the higher your chances of harvesting.
I have not seen any of the statistics that you are talking about for NEM or XYM.
These statistics are available for the Cardano (ADA) Blockchain, but I have not seen them for NEM or XYM nodes. They are probably available, and I suspect that you’d need to be at the expert level of understanding and programing of the blockchain to figure it out.
I am not at that level. I am sorry I can’t be of more help.