Bringing in 2 midfielders, and the world's most expensive defender and a highly rated coach with new offensive ideas looks good on paper as something that can reverse the decline and kick start a new cycle to skip the decline part of the previous cycle.
I think this is a more challenging job than what Sarri can handle. This is not a job for someone who might build a good team in 2 or 3 years. The requirement here is instant success. Even Mourinho would have been a better fit.