Perhaps one small lesson missed?
In the end, as it turned out, it wasn't the gravity mechanic that was too confusing, it was how haphazardly I initially implemented it. After months of playtesting and tweaking the difficulty curve in the early levels, I finally hit the sweet spot (which was measured based on feedback from play testers - mainly family, friends and a few colleagues).
Jonathan Blow did a talk[1] at GDC a few years ago about implementing the time rewind mechanic in his game, Braid. It ended up being a pretty complex system that required a lot of ingenuity to come up with a design and implement it, but the end result is pretty straightforward and easy to understand for players.
However, if you struggle to even describe the behaviour in English then it is a good indicator that users may struggle to understand it too.
I am assuming this is the case here. It may be that the OP had a very clear idea of how the gravity and all its edge cases would hang together but just struggled to code it. I interpreted the article's wording differently.
I do think not being able to simply describe a key game mechanic in natural language is indicative that it may be hard for users to deduce too.