I totally agree with your concern about the 18-55mm being a bit short for a place like Tokyo. I had that exact same realization during a trip to Kyoto a couple years ago. You see these incredible details on the temples or a perfect street scene way down an alley, and you just cant get close enough. It is frustrating to feel limited by your gear when you are in such a beautiful place. Honestly, my experience with the 16-80mm was a huge letdown too. I bought it thinking it would be the ultimate solution for my X-S series body, but it just wasnt as sharp as I needed it to be. The edges were mushy and it felt really unbalanced on a smaller camera. I ended up selling mine after just one trip because the image quality felt like a step backward from the primes I was used to. It was a real bummer. Here are a few things I learned after years of trying to find that one perfect lens:

• Extra reach is basically useless if the images arent crisp.
• Constant f4 sounds nice but can feel pretty dark in Tokyos narrow alleys at night.
• Lens weight really starts to matter after you have been walking for ten hours straight. I really wanted that lens to be the answer, but unfortunately, it just didnt have the magic. If you want my advice, look for a zoom that starts around 17mm or 18mm but maybe from a different manufacturer that prioritizes sharpness over just having a massive range... it makes a world of difference for travel shots.