Yahagi leaving itself wasn't the cause of Naruto collapse as much as his replacements were Hinata fans that wanted her to become the heroine.
True. I remember going back over Naruto Shippuden after the ending to understand why it happened, and what I gleaned from it was that once Yahagi left the themes that were being developed in Naruto and early shippuden slowly began to unravel to benifit what Studio Perriot always wanted to do (among other things).
We started getting dragon ball z level fights that no one could hope to challenge, child of prophecy/fated reincarnation mumbo jumbo, and a alien princess who is in fact connected to Sasuke and Naruto through this incarnation kitten. We literally saw in slow motion an overarching aspect of Naruto get destroyed in the latter chapters of Shippuden for the sequel Boruto.