I think you're missing their point entirely.
It's not about the number of people who have used it. When they say it's "overused" they are saying it's been featured too many times as a main instrument for the enemies goal.
Ever since the Rinnegan's introduction, the story took a turn leading toward first the mysterious leader of Akatsuki and his powerful Rinnegan. Finally after chapter upon chapter of build up and Rinnegan awe, Nagato was revealed and did battle with Naruto. Yet after defeating this long feared threat, the Rinnegan resurfaces shortly after as the main threat once Obito recovered the eyes and it was revealed that the other main instrument, the 10-tails, also relied on the Rinnegan. To add on to all this, Madara is brought back to life with the fearsome Rinnegan. So again, more build up until we finally see Juubito. Now that he's defeated, Edo Madara is still left with his dangerous Rinnegan. He gets revived and loses the eye, only for us to find out that his goal is basically a repeat of what we already went through with Obito: get the tailed beasts, by obtaining what? The Rinnegan. After fearing, dealing with and defeating Rinnegan users so often, some feel like it has become overkill and a new challenge is needed.
Now I'm not someone who believes it's "overused" per se. I can just understand why one would think so. Honestly I wouldn't mind if Madara had new goal that wasn't Rinnegan related. It would make for a more interesting final ending if you ask me