Naruto was heavily criticized during its final war arc, especially when Kaguya appeared. In general, Naruto's Part 2 was never held in higher regard than Part 1, and the same is true for OP. But some time after it ended, people began to look back on the series fondly and found value even in its weaker parts.
The same will happen with One Piece, though its final war arc is unlikely to be as bad. An ongoing series faces weekly, reactionary criticisms. Some of it can be valid; some of it is just fluff. However, it may feel worse now because anime fandoms have become increasingly toxic over the years.