- Apes'king (also we never saw him evil, all beasts were described as pure hatred in the first place. So in the previous times it wouldn't have seemed possible to witness any beast as good)
- even Tobi seems next and soon on the list (because of several hints)
It doesn't seem realistic that all villains will be converted like this. And therefore we wish it won't happen.
On the other hands, what else?
Naruto is always referred to as someone who has something greater than his own chakra and his beast: his power to turn people into good.
The so6p has preferred his 2nd son because the 2nd was preferring love, while the 1st was preferring strength.
It would betray the whole message conveyed by this manga if Naruto was defeating the final villain by overpowering him.
(on a side note, this is the reason why I don't buy the largely accepted idea that Naruto and Sasuke will team up to overpower the final villain Madara)
This rational way of thinking (putting feelings aside, and acting coldly and based on common sense) is done by people like Danzo. Those people don't score good in this manga: I mean that even though they meant good, Kishi takes care that the readers would hate them. Obviously this is not the place Kakashi is meant to have in this manga.
And then, there are too many hints that the transformation of Obito was set-up by Madara. Therefore I can't buy that Obito was just by chance at the proper moment to witness the death of Rin. Look. Even the crush of Obito onder the boulders looks like part of the set-up.