Why would you think that blitz chess online would be the indicator of OTB ability? Obviously, the longer the game, the more representative it is of someone's true ability. Blitz chess is trash for training and competing. There are plenty of players on here with good ratings in 3/0 and 5/0 zergfests who are absolutely horrible when some time and an increment or delay are added to the clock. Blitz isn't even chess.
It depends what you mean by "good rating" in blitz.
I think 2500+ qualifies as a "good" blitz rating. And the majority of 2500+ online blitz players are also experts, or titled masters, in OTB classical chess.
So there's certainly some correlation.
RACE CODE CHESS #RaceCodeChess is attracting the high IQ people. We saw this last Sunday at the first event.