i get what he is trying to say here about peace. if there isn't an immediate threat your reasons for training are different there for your results are different
Athletes that train in the off season don't get nearly the about of production from their workouts as they do as train in season
Look at part 1 and part 2 of naruto, sasuke wanted to kill itachi that was his motivation hell at one point it was his entire reason for living and he trained that way. naruto spent the majority of part 1 try to catch sasuke. The results of those motivation set them apart from the rest of their class
Part 2 naruto was training to get sasuke back, then he was training to get revenge for pervy sage and then he was getting ready to fight to the death with sasuke. the results of that were epic
Now in gaiden no one has these things to motivate them, i mean you could say that they could be training to protect something/one but until now there wasn't anything to threaten them until.
An unused blade eventually turns dull