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.
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.
It's awful. Earthworm Jim and Sonic 2 are both great examples of how the art suffers; and the why is in the video I linked.
The waterfall in Sonic 2 was not meant to look like a fence.