Board Thread:Naruto Discussions/@comment-25188745-20170620121006/@comment-27089028-20170620125656

Hagoromo literally stated it was thanks to Ashura relying on help from others his own powers blossomed. The episodes of Indra and Ashura were poorly made filler just buying time til canon returned.

True, though we never see Hashirama actually ever use other natures and instead just spams wood style every time we see him fight.

That's why I added he was dumb in 'some' instances and as a kid not that he was dumb all together.