I agree with most of the thing you said Rambling, excepted on one point: N, He isn't really your rival, at no point does N "Wants" to fight with Pokemon, at no point N wants to be the League champion. All N Wants is Pokemon Liberation, and the only way he can achieve that is by being the best trainer there is, N doesn't really have any sort of competition with you, N just see in you someone who doesn't agree to his ideas but doesn't look wrong doing so, That's why N wants to battle you, to see who's will is stronger, who is right, Is the actual reality the best thing there is or should it be erased to be replaced by N's ideal. If N didn't need to impose his ideal by being the Pokemon champion, He would never have fought you. At the end, when N understand that his idea where wrong he doesn't even want to fight you anymore, he just leave to try and make the world a better place.
A Rival is just someone you have competition with. and you could agree that N compete with you in the Unova league but he doesn't do it to be champion or the best like you, he just wants the throne.
Anyway to come back to the original subject, i think the first rivals where loved because Jerks are easier to remember than plainly kind person Harsh reality