I read both.
Bleach went blank after defeating Aizen. The mangaka didnt know what to do after beating Aizen (no Bankai for Aizen, and here you are comparing it to Naruto?).
Kishimoto brilliantly planned the 4th GNW. Power creep is bound to happen in 500+ chapter series.
One Piece did it worse. I will accept power creep everyday over holding back characters that the author hyped 20 years ago.
Naruto's each and every protagonist and ANTAGONIST beats One Piece's pro+antagonists.
I have got some free time. We can do a character by character comparison and an arc by arc comparison. Lets determine rules first (personal opinions does not matter).
Then we can see which series come out on top.
@lee33