The oil you "Used for years" or what anyone else has "Used for years" has no bearing today. Oils have changed in less than 12 months, much less years. You can "get by" using some oils or, you can do as I did with me Wing and, my other bikes, use the proper oil for the application.
Even though the Wing has probably the best transmission in the M/C Industry, you can feel the difference in shift quality using a Premium Synthetic M/C oil such as AMSOIL M/C oils or M-1 Racing 4T.
I could be wrong but, I don't think there is anything that says Rotella is "Approved" for M/C use, just that it can be used. And Rotella has no True Synthetic, they are Group III Base Stocks and Shell's MSDS state 92-98.9% Petroleum. Is it a good oil ? Yes. For Diesels...
A High quality M/C oil will have a high TBN, Higher amounts of ZDDP for cam wear, Specific additives for clutch performance, higher Anti-Rust and Corrosion Inhibitors and Specific additives for the transmission...
Oil, is the Life Blood of youe engine. The Oil Filter, is the Kidney that keeps it clean.
Regardless of Brand, Synthetic or petroleum, I always recommend a M/C Specific oil with a JASO MA Rating, better yet, MA 2, but never MB.
If anyone says that there is no difference between M/C oil and auto/diesel oils, they are misinformed.
Bob