Rem atonia is paralysis.

Maybe you should try collecting actual data from lucid dreamers. Create a poll and ask people if they experience paralysis at any point during a WILD. I think most people do, and I think your assumption that most WILDers are going to be like you and not experience some sort of paralysis is inaccurate. Also the fact that people are more likely to experience SP in between WILDs, just shows that there are subtleties involved here that are not so black and white as you are trying to make things seem. It is not unusual for a term to be used incorrectly. Consider subconscious and unconscious. The correct term for what most people refer to here as their subconscious is unconscious. But it's generally accepted that people are more familiar with the term subconscious, so that's why people continue to use it, for purposes of understanding.

Sleep paralysis is simply a condition that results from awareness that REM atonia has continued longer than it should have after waking, or awareness of REM atonia paralyzing your body as it prepares to dream. Therefore sleep paralysis is a direct product of REM atonia. The terms overlap. It's not quite as simple as you are trying to make it.

I'm all for the promotion of using the term REM atonia in place of SP for WILD tutorials and such, but you still have to acknowledge that SP is, for many people, still a part of WILDs/LDs and not dismiss it as merely some rare medical condition, because that is untrue. The majority of people I have spoken to here have experienced SP at some point.