I fail to see how 90% of panel time dedicated to babysitting Momo and the bomb diffusion side quest would all of a sudden be seen in some "useful" panel time if Yamato joined the crew?
how she came to meet oden ,
also included a flashback with the samurais that helped her get through a short stint in prison. The way I see it, we get to see just enough of the character to fall in love with them before they join.