i didn't mention sasuke's abilities because the post i was replying to was saying that combining sm and km would be nearly useless. on the contrary, i think the combination is key to fighting on a par with sasuke.
both have weaknesses against each other tbh. naruto has been shown to struggle against genjutsu, and has no jutsu to piece a final susanoo as yet (maybe he can pull him out with chakra arms like gaara with sand, but that's an argument for another day). sasuke, on the other hand, has lower stamina even vs base naruto, and him struggling against speedy opponents is a recurring theme.
now, to your arguments. the bit about the chakra sensing was for me to make the point that naruto can track opponents very effective, and know the enemy's position, so he can't be caught off guard or sneaked upon, or hidden from. the threat perception gives him early warning of attacks, without blind spots.
nagato said he could easily control naruto at that range, so he definitely didn't expect to be overcome. he stabbed naruto in sm, not in sm+km. naruto awakened the combined mode later. and jiraiya had great chakra control, as evidenced by the fact he could perform a rasengan with one hand. him not having a perfect sm is irrelevant.
about the frog kata, could be, but since he mastered both modes i don't think he would need another training arc for something which is effectively the same. he didn't need an arc for the mini-rasenshuriken and other variations for example. and neither did sasuke to master enton.
now to the defence. yeah, both alone are vulnerable, although naruto's sm defence is better than jiraiya's. its hard to know exaactly though as he's been shown getting hit in that mode extremely little. sm was pieced once by nagato, km naruto was 'hurt' a few times, although he's managed to stop swords and the like and tank raikage hits without evidence of physical damage.
but the combined defense, a massively increased durability + the chakra cloak, that will take something special to get through it, especially physical attacks. do i think it can tank amaterasu or a susanoo arrow, no. but a chidori, yes. obviously some other jutsu like kamui or tobi's warp, it doesn't matter how strong your defence is. it's still vulnerable to a lot of techniques.
but as far as strength and stamina goes, yeah i think 'the sage's body' is an apt comparison, even though he may not have reached the level. madara and nagato had the sage's eyes and they were not of his level either.
anyway, my whole point is that far from being irrelevant, km+sm will end up being greater than the sum of the parts.
