All what Lupe is saying is no different to asking the question, "who's the greatest rapper of all time?" etc
In order to quantify it, you need to set the parameters of how you want it to be judged. and then once you set the parameters, you still need to give weightings to each criteria, as some should hold more weight than others.
For classic example, the criteria of album sales/number #1s/gold, platinum plaques etc.
It we take discography and catalogue into the discussion, then do we look at it solely on albums (i.e. commercial released body of work) or overall quality of substance of songs released? If it's the former, then Joe's point is clearly a valid one but is it really right to look and critique Jay E off of this latest project? So we gonna dismiss all the songs prior which weren't commercial releases or in album format - let's be honest, if Jay E wasn't a mastery prior to Written Testimony then why was there so much anticipation for him to drop the album in the first place? There's truth on all sides, but for Joe to completely dismiss Jay E in any convos with the elite and top tier rappers is IMO naive and asinine