One reason Biggie Smalls is overrated is because he only had the time to make 2 albums, he never tainted his career with any "bad" music, the same way money other artists had. A lot of people believe that if say Nas had died after dropping his second album, he would've seen the same praise as Notorious, but of course he didn't, and he went on to release the album that many believe ruined his career, Nastradamus. Now the question is that if Biggie Smalls were still alive, would his quality of music deppreciate over the years?
Probably yes.
In the words of Jadakiss from the song Shootouts: "Controversy sells, but it ain't like death".