I was just thinking about this. Kishimoto really could have used a new arc in PI (right after the Konoha Crush, but before the Akatsuki appear) where he could have taken on the following:
A) Build and flesh out Naruto and Sasuke's friendship unambiguously.
B) Lightly tease Sasuke developing genuine affection for Sakura beyond that of a friend or teammate. Also have Sasuke tell Sakura (and us) what happened to his family much earlier on.
C) Do some world building. Send Team 7 to the Hidden Sand (only 3 days away) with a different leader - Kakashi has to stay in Konoha to do paperwork alongside the Elders as there is no Hokage now, as well as eventually confront Akatsuki. The leader should ideally be Kurenai, who otherwise is vastly underused and also can get Sakura AND Sasuke started on learning actual Genjutsu, as well as help Naruto at least improve his chakra control so him learning Rasengan so rapidly makes more sense in the arc with Jiraiya.
This could also be a great opportunity to explain using and fighting Genjutsu. It's not like Jiraiya's training really did anything for Naruto in that regard anyway, IMO. Kurenai's training could have easily replaced it.
Basically, Team 7 + Kurenai have to go to the Sand to take a highly classified scroll to them that essentially is a sign of trust and good faith, reigniting the Leaf-Sand alliance after the betrayal of the latter village. This could also be an opportunity for Naruto to actually MEET and properly befriend the (reforming) Gaara again before PII, making their friendship later on far more realistic. Even have Naruto bring up how he wants to be Hokage and then have Gaara realize he should try to be Kazekage like his new friend and rival.
Could also be a way to flesh both Kurenai and Gaara out, naturally, as well as introduce the Hidden Sand proper and tackle the themes of war and peace a lot earlier. Maybe even have Gaara be a little more tentative in his redemption for now and still a little too brutal against perceived threats (but ultimately far better than before as a person and in mental health), so his evolution comes across as more natural when we see him again.
D) Give Sakura and Kurenai fight scenes where they actually get to throw Genjutsu around and destroy some named Chunin and Jonin, respectively, in fair fights.
E) Not Team 7, but back in Konoha and during this time, give other characters more development too. Have the Hidden Rock send a small force to further destabilize the weakened Konoha (making the need for a new Hokage VERY apparent).
This can be the source of many good fights and development for Tenten, Hinata, Ino-Shika-Cho (who were kind of a failure as a team in PI), Kiba, Genma, Raido, and Asuma. Probably also tackle other plot points line making Hinata finally stand up to her father and call him out for his abusive behavior, as well as Asuma regretting he and his father weren't able to reconcile before the latter died. Everyone should get Ws here and get to show impressive techniques or stats, maybe Genma and Raido aside.
F) Not really a new arc, but kinda change the circumstances of Sakura and Sasuke's last meeting and what happened later. Have Sasuke actually take Sakura back to her room after KOing her, or at least ensure she is found by trustworthy ninja before leaving instead of leaving her on a bench...even risking jeopardizing his escape somewhat.
G) Also not a new arc, but as another poster suggested, add a new Sound 5 member (making it the Sound 6, which also sounds better due to the alliteration) who Sakura actually beats, but is too injured and weakened against afterward to go and back up Naruto.
