They're are on beat. They are actually on the true tempo of the beat, most rappers rap in double time(half the tempo of the beat). Tap out the tempo and you'll be able to catch it
I used to come to this song just to see how iff beat it was but know I found myself liking the song, its not offbeat, its just loaded with words, its actually hard af, like this is my favorite song now... fav line is “ your will never catch me out lacking without 10 bands, I think i lost my mind I spent a thousand on a pair of pants