He was also proficient in EVERYTHING. And performed on a Jonin level. You argue Gaara could destroy a village, no. Shukaku could destroy a village, Gaara is on par with Rock Lee. Naruto wasn't on par with either, Gamabunta was. All Naruto had in those moments were chakra, enough chakra to summon Gamabunta, and enough shared chakra to use a transformation jutsu.