Thanks, I somehow took it as something during the Pain invasion...
Kurama's chakra is his life force, it regenerates, I don't see the threat in doing so. It had two jinchuuriki before Naruto, both not talking or treating it in
pleasant way there comes a third one, trying to do keep him under control even more. Of course it would try whatever it could to fend itself, who wouldn't?
After a hundred years of slavery, after it finally got free of the struggle, it just happens to be sealed away again, so of course it would try to act out again, when it could. Because of the long isolation and time it began to use it's hatred to fuel it's powers, likely similar to how Sasuke did during the Danzou fight. But it wasn't hatred itself, it wanted to rage because it was treated badly after the father was gone.
Within a rather short time he got to see how other biju are better, see the difference of Naruto to others, realize their parallels, and start to support him. So it took a couple days or hours within the manga, so what? It's not impossible, it happens in reality too, like it or not.
Would I have liked to see a alternative where the bad monster stays evil until the end? Yeah, why not, but those types of inner monster can be seen in so many other manga already too, it wouldn't be suprising or original.