Orochimaru got away. Unpunished for all his actions.
Kabuto got away. Unpunished. And better yet placed in charge of an orphanage with literally an army of Mangekyo Sharingan kids and a giant one.
Karin is more mature than Sakura. She literally could not bare Sasuke leaving her again. All she wanted was the nuts. Karin just wanted him to be happy regardless.
Entire Gaiden was unnecessary. The point was for Karin to be the mother. Not Sakura. No reason Shizune couldn't have just said 'Sakura is your mom, you were just born outside the village'. There is no excuse for her not just saying that.
Karin keeps Sakuras umbilical cord in a glass showcase in her drawer. First of all- why. Second of all, why would Sakura not have it?
Sasuke didn't kiss his own wife after being gone for 14 years. He didn't hug his wife after being gone for 14 years. He took his lunch and walked away without saying I love you for probably another 14 years.
We never got closure of what happened to adult Shin. We just don't know. He probably died, yeah. But it's poor writing to not confirm it on screen since he was the main villain of the arc.
Whoever was Hokage at the time, Naruto or Kakashi, it doesn't matter. They allowed a pregnant woman, Sakura to leave the village safety and fend for herself to find Sasuke for 9 months until she couldn't find him, and had to give birth in Orochimarus hideout.
Instead of letting Sakura go, why did they not send out the anbu black ops to find Sasuke? Surely they would have had a better chance.
We have to just accept that Karin happened to find Sakura 'by chance' and assist her on her travel since it wasn't explained how they met.
People will defend this.
1. Kabuto was izanami'd. He has a complete change of heart and was placed head of the orphanage he deserved to lead. He is no longer a villain.
2. Karin has not been proved to be more mature than Sakura, hell Sakura raised a child by herself. HOW MUCH MORE MATURE DOES SHE NEED TO BE???
3. Gaiden was unnecessary true. BUT IT WAS ONLY AN INTRO FOR THE MOVIE, nothing more.
4. The umbilical cord was just there since the birth. Umbilical cords keep important information about the fetus and its not uncommon to keep it for research.
5. Did you honestly expect more from Sasuke, a true Shinobi?
6. Adult Shin was ignored, i give you that. More than likely died at the hand of his sons.
7. We both know the Hokage did NOT approve her leaving the village to search for Sasuke. Hence why she reached out to Karin for assistance.
8. Again, it is probable that Sakura acted on her own and not under the approval of the village.
9. Karin probably found Sakura lurking around one of the hideouts looking for Sasuke.
All of your Rant points seem to be easily explained by the Plot no jutsu.