This is partially right, and partially not. Motion Lighting came into being because it does much more than RM in its specific motion lighting use case. To accomplish what a single ML instance can do would take numerous rules -- what a pain that is, especially when you want to change something.
The "performance" issue about RM is blown out of proportion in many posts. It incurs an additional overhead relative to Motion Lighting of around 75 msecs. Ironically, the most time sensitive automations are motion lighting, as we see the result -- it's in our face. Most automations are not that time sensitive, and it doesn't really make much difference how long they take. Consider for example, changing mode or changing a thermostat setting. These happen infrequently, and who cares about an extra tenth of a second?
But, as many of you know, I'm a big believer in the KISS principle for home automation. Simpler is better than complex, less is more. I only use RM for weird stuff there is no other way to do, and none of my rules are very complicated. Having said that, I agree, its UI can be a pain point. However, what it does is non-trivial, and a new UI will someday be a major undertaking, to say the least.
