I dunno I don't buy it. I'm getting guys who are 1900s and are like 1200 highest across rapid/blitz/bullet. Ok yea the opening book and stuff fine we both use it. But every game goes out of that book at some early stage and usually the position is even and these 1200s can find moves and maintain wins over 2000s etc just because it's slower? Bullet rating whatever some people are slow and bad under time pressure. But u are telling me that someone can play at least a middle game and endgame at 1900+ level and can't get a rapid or blitz above 1200???? No! Don't buy it. Blitz and rapid aren't that fast people!!! I'm pretty sure there's foul play.
I am above 2000 in daily in 1250ish in rapid( probably a bit under rated). In rapid I make more mistakes, but if I have some time to gather my thoughts I can be quite strong. When I use the analysis board and opening books I am even stronger.
I think it is, because in daily games players have very different approaches what to do with their time. Some players think carefully about every single move and end up spending multiple hours on a single game. Other players (usually high rated in other modes) seem to use it to just play A LOT of games at the same time and blitz out moves very fast.
In the other modes both players usually make use of the same time (or at least try to^^), in daily games there are huge discrepancies. Im very sure if all players spent a lot of time on daily games we wouldnt have those huge differences in rating. By that I dont mean they should, I'm perfectly fine with everyone using this mode however they want. It's just my attempt for an explaination :-)