how about i super spoiler all of this SPOLIERS!!!!!! THERE ok well thats true that he is a threat so 1 he was holding back in the naruto vs. sasuke fight because he kept saying that he wasnt gonna kill him and sasuke was going the oppposite so he was fighting with almost no kyubbi, 2 naruto has yet to use the full power of the kyubbi because the tails will increase with the power to a maximum of 9 and wayyy later in the series it takes orochimaru and jiraya just to hold naruto back with only 4 tails! so 3 nauto is a extreme threat because so far in the series we have only seen him with 1 tail and he is extremly powerful like that so here is something i did in my spare time
1 tail- = with garra 2 tails= with form 2 sasuke 4= tails more powerful than jiraya and orocimaru put together 5= to about the same as yonadime (naruto's father, 4th hokage, and now leader of akutsuki) 9=????instant death to the world and every single ninja in it?
PS he has barely awakened the power because he can only use it when his life is in danger unlike garra who can summon it when he needs to so that is another factor to consider