That's not a feature if you don't want to use a shared pool though. I had to specifically ask them not to "upgrade" my room because none of the "upgrades" are an objective upgrade path whereas at a property like Suiran it's pretty clear that as you go up the room hierarchy the rooms just get better and you don't lose features. For me losing the bath positioned with the doors opening up to the garden would be losing the key feature. It would be like if at Suiran taking an upgrade meant losing the outdoor onsen bath, it wouldn't necessarily be an upgrade at all.
When this hotel first loaded rates they loaded them far into the future at the exact same price for every single night. I booked as far as I could given my plans for trips and I booked every night individually so I can just tweak them however I like.