I may be wrong, but from what i know, the reason Giyu is upper 4 while Muichiro is upper 3 is because: Demon giyu says he only eats humans when hes starving. And demons get stronger the more humans they eat. So Muichiro most likely has ate more humans than Giyu, placing him a rank higher.
You said all the hashiras are there then where is tokito? Or is this another era where tokita was not a hashira yet? But I really liked the videos you make<3