IMO it’s actually fine in series, not just anime, in general. There is a formula for each series that work for them. You watch the series if you like the formula.

On the other hand, I hate this for a lot of Hollywood films. A lot of them share the same formula, it’s not even fun to watch.

I won’t even try to reach One Piece, there is Detective Conan. Every episode is the same for 30 years yet they still make it and people still watch it. Why? Because the formula is good.