Oda said what he likes the most is create characters. And if he could he would focus more in them than what he already focus. PH was planned to be two arcs. So he will always create new characters until the end of the story. Let's hope he can manage better the screentime in the next arcs
He's had a habit of doing this a bit too often since Marineford, and even more so since Dressrosa. Before Marineford, I guess the strongest example of too many characters were in Water 7, but they were all balanced out in a way that it actually served a purpose, to keep you on your toes as to who would be the Straw Hats' new shipwright. Marineford, I can at least get that it was trying to show off just how large and varied the marines and Whitebeard's forces were even if the war was a bit messy, Fishman Island was a bit of a red flag what with the useless Medak Quintuplets, the mermaids whose only purpose was to introduced that godawful nosebleed sideplot, Shirahoshi's useless samba brothers, and Camie and Hatchan being sidelined, among other things.
With Dressrosa and onward, it just looks like Oda is trying to see how many characters he can shove into panels. Even the Straw Hat Grand Fleet outside of maybe Leo haven't really been that relevant. WCI was just as bad, but Wano really took it way too far, especially when it came to giving side characters even more screentime and introductions. Thankfully for Egghead, there's fewer example of this, but the arc has too many other problems going for it.
I often get the feeling that this is just Oda's way of making up for the fact that he never got a chance to make other manga stories like he wanted. He always said he wanted to make a giant robot manga after OP ended but that was no longer possible for him with his health and schedule. So it feels like all of these excessive side characters and even turning Luffy into Nika feels like his way of trying to give new life to the characters he never got a chance to create for other stories.