Wdym? Kyubi's intervention against Pain was the most logical time for Kyubi to help Naruto ever. The other times it happened was utter nonsense.
I have numerous problems with that fight :
- it’s the beginning of power inflation : Naruto managed to learn Sage power in less than a week, while it was clearly said by Jiraya to be extremely difficult. And Naruto didn’t even need the help of the elder he managed to do even better than Jiraya. In like 4/5 days. Ridiculous.
- Kishimoto changed his plans and went from Tsunade fighting Pain to Naruto saving the day. So he had to made everyone cheering for his return to save the day. Ridiculous too. they were ninja and powerful, waiting for a teenage boy who was half trained to protect the village was stupid.
- Pain was much stronger than Naruto. First he needed Kyubi 8 tails to weaken him. And then his father help inside Kyubi to free him from the fox. Pain was the leader of a powerful gang. He should have been above Naruto pay grade.
- The end was quite cheap with all the clones.
- The end with the talk no justu wasn’t really good.
That fight was the beginning of the boy savior Naruto and with it began the worst part of that show.