You're all just making conjecture and mis-interpreting the manga completely.
Even if the the transmigration meant in terms of talent (which it doesn't), nowhere suggests that Hashirama was a prodigy. He fought every single day from a young age and managed to survive till the post-era of the Warring States - that itself is going to bolster his power and skill. Secondly, who knows how much or what method of training he used/did? We don't, so stop making presumptions.
Thirdly, when Hagoromo talked of transmigration; he meant their chakra and will. Hashirama, like Ashura sought for peace throughout his life and believed by uniting people through cooperation, peace could be achieved. Also, Ashura did at some time in his life, "awaken" his own power, and that would be directly inherited by Hashirama.
Even if the the transmigration meant in terms of talent (which it doesn't), nowhere suggests that Hashirama was a prodigy. He fought every single day from a young age and managed to survive till the post-era of the Warring States - that itself is going to bolster his power and skill. Secondly, who knows how much or what method of training he used/did? We don't, so stop making presumptions.
Thirdly, when Hagoromo talked of transmigration; he meant their chakra and will. Hashirama, like Ashura sought for peace throughout his life and believed by uniting people through cooperation, peace could be achieved. Also, Ashura did at some time in his life, "awaken" his own power, and that would be directly inherited by Hashirama.