@Isekaijin
Exactly, instead of story development it seems more like
just author pick. At this point all sisters have done a lot for him and they got own share of misfortune in life. Also if like now choice isn't from plot progression author could just end it at Kyoto trip arc.
I like to compare this to Agatha Christie
"Guess Who?" story type , but instead of murderer you have bride. And sticking with this comparison, here all clues instead of hinting final girl were used to justify author decision- who played
way too safe for the most part, leaving it so open.
I don't say manga is bad or something like that (like I said at the moment 7/8 out of 10 for me), but it should be point out.
Details and writing like this makes difference between just good story and very good/ excellent.