"Kurama has lived for hundreds of years, so he is automatically more smarter than Naruto."
Dumb logic. Black Zetsu has lived almost a thousand years, yet he was constantly getting out-smarted by Naruto during the final battle.
Momoshiki and Kishinki has lived more years than anyone bar Kaguya, yet he was out-smarted in battle by Boruto who barely has any battle experience.
Fukasaku who has lived more than 800 years, got completely out-smarted by Nagato who has barely lived 30.
The point? The instance of someone who lived and fought for a colossal amount of years doesn't necessarily imply such person is always going to be smarter than someone who has lived less. In fact, the experience that comes with living for long periods brings pride, and condescension. Both of which are catalysts behind the eventual fall. Furthermore, "battle smarts" only matters when your opponent is trying to be smarter. In a battle where the opponent induces unpredictability to his or her moves, the need of trying to out-smart such a person is difficult, since they aren't exactly trying to he smart. Unpredictability is a very difficult skill to utilise for the reason a user has to be able to camouflage their intentions. Hence, why Naruto is generally smarter than those he has fought against, since he constantly has to improvise so the viability of his plans is increased.