They could've kept Jiraiya alive and he could've died an old man seeing Naruto become Sage. I wasn't questioning the development of Naruto, the fukking show is called Naruto....everything is about him developing as a character.
People hate Obito because he's the deus ex machina, in general, people hate DEM's due to forcing the plot to take a sidestep (Avatar) and because it shoehorns in a plot that's irrelevant. Its no surprise really, its been going on since the Star Trek days.
He doesn't act like the masked man, he acts like a child once the mask comes off. He goes from being the mysterious and ruthless antagonist to just spending the entire time arguing with Naruto in a whiny fashion. Always with the same pouty face. He's basically like a 12 year old in an adult's body. Which is the second time he's acted like that in the series, except the first time was him putting on a front for the ruthless masked man.His entire back story is riddled with plot holes with large portions of the story missing.
He shouldn't even be in classes or on a team with Kakashi, because Kakashi was supposed to graduate at 6. Which is physically impossible, given that the entire backstory is how they were always together and how Kakashi became a Chunin a year before Obito (Obito surely was not 7). His entire story within the Mist Village is completely brushed under the rug. We never find out why he went there, why he didn't immediately capture the 3 tails, how he put Yagura (a perfect jinchuriki) in a genjutsu, nothing. It's not even like they showed a flashback that doesn't make sense like Kakashi being his age, they acted like it didn't happen at all.
His turn around is basically just an exact copy of Nagato's story. He was used by somebody higher up than him, so he wanted to do something to help out and now he's become a good guy. I mean, he even attempted to do the exact same thing Nagato did before being interrupted. But it's just not done on nearly the same level. Nagato and Naruto had deep ties to each other. Both had the same mentor, Jiraiya was Naruto's family (revealed to be a literal connection), etc. Obito was just some random guy, Naruto didn't even know who he was for more than a couple hours. But because of a little bit of back and forth, now all of a sudden they're best friends and Obito apologizes for everything. And it wasn't like Obito lost and that's what started the turn around after a (corny) speech by Naruto about his past. Obito always had the sentiments and never truly believed what he was spewing out. He always deep down still wanted to be that kid who became Hokage.
Couldn't die because the plot was always tailored to keep him alive. He gets stabbed in the heart, nope, he can still keep it moving and control what he's doing to save himself. Which is iffy, but not really impossible to be fair. He loses all of the Tailed Beasts, something we have always been told his sure death unless you are an Uzumaki. But wait! This one is different! Because he's the Sage, he can stay alive and just can't move for a while (even though he begins moving like, 5 minutes later, however little). And then we get to Kaguya. Where apparently Naruto and Sasuke can barely move, but Kakashi and Obito can do 50m dashes to save them by being led by the vision of a 12 year old dead girl. He gets stabbed in the stomach, disintegrates, and then comes back the next chapter on some spirit world shyt. Which makes no sense that chakra connects both worlds, and if it does, why has nobody come back before Obito? And then he dies again, finally. On top of that, we have him getting crushed in half and living, which is iffy but again, can make some sense given anime physics. And you have him spamming Kamui, which never makes him go blind and never messes with his chakra. Which isn't even attributed to Senju DNA, that's just the fan reconciliation for it.
It was needed for Naruto to learn Sage Mode and become acknowledged by the village. It actually led to development of Naruto's character 
They completely ignore that his motivation was Rin only until he learned the truth about what happened.
He kept arguing with Naruto because he kept nagging him with his stupid friendship speech. Plus he was having a real conversation with Kakashi for the first time in like a decade? Of course he's not gonna be acting like Madara through all that.
