. . . Not that Dragon Ball Super was any better or worse than GT, for that matter...
In many ways, Naruto had already gone down hill, considerably, after the Chunin Exam arc. It recovered, somewhat, during the opening arc or two of Shipuuden, then started to taper off before plunging off a cliff at the start of the ninja war arc. It's no surprise why, regular release schedules leave little time for plot development and an author may have a decade or more to define how their story starts and works before getting to write the first several chapters.
This is why short series developed in isolation or off of light novels are often vastly superior. Madoka Magica, Fate/Zero, Kill la Kill, etc - these are all excellent productions which focus on a relatively singular plot arc (spare for Fate/Zero, which is just a masterpiece, best tragic theater production ever made). The longer a series drags on, the harder it is to keep it going while hiding the fact you are effectively repeating the same sequence of events every other arc.
