The reason why Naruto has been on top (last week and this week) is because this chapter (as well as the one before it) featured the return of most fan's favorite characters back into the main serie.
No its not.
These rankings are in respect to the chapters from 8 weeks back, not the most recent. So for naruto it would be the Juubi awakening (And Kakashi doing stuff), while OP would be the chapter that heavily focused on Brownbeard, and Ceaser laughing at Luffy while expositing future plot points.
A strong-ish Naruto chapter and a weak OP one.
Assclass slipping a little isn't surprising since the novelty of the teacher and the premise in and of itself can't carry it forever, and the chapters were pretty repetitive and straightforward for a while there.