It might help with Mashu's progression, but X to doubt on Mount-fuji circle. I think if FGO was written to be more of a proper interconnected story and more weight and care was given to say the Epic of Remnant period where Mashu couldn't really do anything, you could've leaned into Mashu going I have to do it all for senpai and bring it in harder with a separation like this.
Still it might turn out pretty ok.