Ashura's Yang chakra transmigrateded , but Hashirama is still Yang type.
If you look at edo-Hashirama who has no more Ashura's chakra , he is still able to give life to a living forest , use his most powerfull Mokuton jutsus without Ashura's chakra.
Hashirama is a very strong Yang type ninja even without Ashura's chakra.
Hashirama is a huge source of Yang power.
That's a kekkai genkai, as explained by yamato it was his unique release of water + earth chakra
no doubt hashirama had explosive chakra and im certain ashura had a major part of it, as naruto even for an uzumaki has pretty good base chakra
and i agree with your logic fully, just i dont see hashirama in comparison to sasuke's yin, due to the fact it more than likely needs to be compatible with yang of a similar nature such as naruto
otherwise why did the yang not manifest as it did in Madara in at least both eyes, and sasuke receiving the one eye powerup from hagoromo