Guys that took sets off of 2011 Djokovic:
AO: Ivan Dodig
Dubai: F. Lopez, Berdych
IW: Fed, Nadal
Miami: Nadal (the final went to a decisive tiebreak; Nadal wins that breaker, there's no "streak")
Madrid: Ferrer, Bellucci
Rome: Clayray (had him in serious trouble in SF, decisive tiebreak)
FO: Delpo, Federer (3)
Wimbledon: Baghdatis! Tomic! Tsonga, Nadal (I say 2021 Djokovic definitely better on grass)
Montreal: Mardy Fish!
Cincy: Monfils, Murray (2)
USO: Tipsarevic, Federer (2 and was down match point on Fed's serve), Nadal
After the USO, we typically give him a break or a free pass, but he was not the same player after USO.
To his credit, Djokovic was competing against a stacked field in 2011 and winning virtually everything, but let's not forget that Murray almost took him out in Rome and that Fed was a net cord away from knocking him out of the USO and going 2-1 against him at slams.
Again, I'm not saying that 2021 clearly better, but we tend to romanticize 2011 Djokovic the way we do with earlier versions of "prime" Fed (who lost to Murray and Rafa on HCs numerous times).