It's a tradeoff between reaction speed and the ability to read larger amounts of objects at once. I've never flat out said "play hidden because it makes you good", i was suggesting that for some people, hidden may help train your eyes to stop following notes down the screen. That specific issue is something I had a lot of trouble with, and I found that in my case, trying hidden was a useful way to retrain myself to not do that.
Just like scroll speed is personal preference and no one speed works for everyone, the same obviously goes for reading mods. Some people will never really adjust to them, while others may become so accustomed to them that they literally cannot play without the vision mod.
However, the actual issue at hand here, following the notes down to the bottom of the screen (or top in the case of upscroll players), will have some effect on a player's ability to read. If you assume the same length of time is required to read a pattern regardless of where you focus on the screen (which appears to be a reasonable assumption), reading closer to the receptors/judgement line leaves you less time to correctly read the patterns and react, which is very likely exactly what is causing Edz problems, just as it caused me similar issues.