i never found him all that strong in base tbh, the only reason he beat kakazu was plot and to show the power of rasenshuriken. id say high jonin or low kage at best.
low-mid kage definitely, tsunade is low kage so that puts it in perspective, don't forget kakashi is kage level too, and kakashi said himself naruto surpassed him awhile ago.
Base Naruto is a straight up beast. With only a tiny bit of chakra from Kurama that was even less than the chakra he had in base he was ablee to make 100 clones with Oodama Rasengans that destroyed Hashirama's strongest mokuton tech. Not to mention aganist Pain he was able to make 1000 clones in base that withstood shinra tenseis. You people dont give Base Naruto the credit he deserves he can beat kages like Mei and Tsunade in base.
After he had been weakened by the others. Even though Naruto was beaten up himself, he had to be saved by Yamato once before he landed the FRS blow to him. If he had faced him at full power, it would have been a completely different story. Overall, he just isn't as smart as any real jounin would be.