So Kishimoto really did a Bad Work Showing Sakura loving Sasuke into a point she was willing to abandon Naruto and the Village to follow him and "red herring" pairing become most popular than the main one.
The SS moments and mainly the chapter 181 was extremely unnecessary for a shonen manga.
Puting Hinata in this love triangle by making her declaration too.
Like i Said the big three pairings had chances.
Kishimoto tried to secure the pairing fans until the last moment in this messy.
About the Heroine and love interest thing.
Bulma was the Main Heroine in DB she didn't ended up with Goku.
Sora was the main heroine in Digimon and she didn't ended up with Taichi (Ironically these pairings remembers SS with the Main Heroines marrying the Rival)
Rukia was the main heroine in Bleach and didn't ended up with Ichigo.
Nami in OP didn't care about Romance much less Luffy
This argument doens't work very well.
I guess Kishimoto could have made a open ending if the shippuden continuation still was focused in the current generation.
But since Boruto needs Ccildren. Kishimoto was obligated to decide pairings. But Kishimoto didn't count Ikemoto incompetence to write and drawn. I don't know to which degree Kishimoto is envolved and "supervisioning" Boruto. But Boruto sucks...
Kishimoto seems to be the Boruto manga's idea guy. If ikemoto gets stuck he asks Kishi and he gives him an idea off the top of his head. Or. Ikemoto gets an idea for his story Kishimoto gives a justification to make it work.
Apparently the opening scene was Kishi's idea. Which admittedly the casual anime watchers I know said that it actually got them all interested after first. Before its boring story drove them away. He also probably push the cyborg ninja and the scientific ninja tools as he wanted to do a sci-fi manga but he was stuck on Boruto for awhile.
Beside that what is most likely:
Karma seal. Ikemoto makes it, kishi probably justified why it looks like Tsunade/Sakura's forehead seal. Theirs is based off it.
Baryon mode. Ikemoto wanted a new one wing angle super mode transformation for Naruto. Kishi thought up suicide nuke mode.
Shinjutsu. ikemoto wanted new abilities that would make his characters better than Kishimoto's. Kishimoto probably helped come up with the concept.
Though it is basically a guessing game of what came from who.
Yes, and that scene is portrayed negatively and showed how badly her feeling for Sasuke were influencing her in a negative way. That way to show how much Naruto's influence was a positive on her.
The big three parings was a Western thing Kishi didn't know about until years into the story. Hinata was not important to the story until Kishi's first editor Yahagi was replaced right before the Pein arc.
You chose ones that already knew about the Heroine/love interest understanding and tried messing around with it some even still suffering for it.
One Piece. Nami is still considered the love interest of Luffy. From what I understand even somewhat officially. Just they aren't interested in doing anything with that because Oda both doesn't want to focus on that type of romance and saw what it did to Kishi.
Digimon. intentionally went against it and constantly has to deal with people not being over it. To the point that the mess that was Digimon Tri, was an attempt to deal with it.
Bleach. Kubo always wanted Ichigo/Orihime & Rukia/Renji and made it pretty blatant throughout the story. Even then before heading off the final battle the story had to repeatedly beat it into the readers head those were happening. Also if their is a sequel continuation. I think it pretty clear Kazui will be the lead and Ichika will be the love interest/heroine
Dragon Ball. Originally a one arc story about a boy and a girl traveling a mystic land in search of wish granting orbs. Romance was not intended...at least between those two. Toriyama had to basically force Chichi onto Goku because that's was the only way he could perceive Goku getting with anyone. Also during Gohan's brief stint as the Hero, he almost immediately got a Heroine/Love interest with Videl. Also, Trunks focus arc right now? Love interest/Heroine is Mai.