Man Nagatoro's story kinda reminds me of Sasuke getting pissed that Naruto just seems to be getting stronger and stronger while he is barely getting stronger, back during OG Naruto. Kakashi tells Sasuke something along the lines of him being at lvl 50 while Naruto is at Lvl 1 and so of course Naruto will seem to be getting stronger faster. It is because Sasuke was just way stronger than Naruto to begin with, and thus it takes more training to raise his current lvl than Naruto. I kinda have a feeling that Paisen will say something along those same lines to Nagatoro.