The Megadrive had native RGB output, you just needed the right cable and TV. Maybe that was not common in the US, but it was in Europe; heck, the French model ONLY had RGB output.
All Genesis models were capable of RGB, but almost everyone used the component and/or RF adapter. I own three American genesis models and have yet to ever own a proper RGB adapter for one.
I know, but the world is not only the US. Europe had SCART and pretty much every TV supported it, and Japan had RGB-21 (same connector with different pinout), but I don't know how common it was.
If you have not tried your MD/Genesis with RGB output I would recommend you to try it, the difference in picture quality and clarity is amazing.