Like someone mentioned, that high-res sensor really shows everything. I went through this exact same thing and honestly im so satisfied with the Sigma 18-50mm f/2.8 DC DN Contemporary for Fujifilm X. It handles the 40MP perfectly without breaking the bank.

• super light for travel
• constant f/2.8 for low light
• way under $600 I saved enough cash for fondue in Switzerland, which is a total win.

You 100% need the Tamron 17-70mm f/2.8 Di III-A VC RXD for Fujifilm X! It is absolutely fantastic on that 40MP sensor because it resolves way more detail than the old kit glass. The built-in VC stabilization works amazing for those low light shots in the cold! Its super sharp with a constant f/2.8 aperture and fits your $900 budget perfectly... seriously, you are gonna love the images!

I'm very satisfied with the move toward newer third-party glass for that high-res sensor. From a technical standpoint, the resolving power is just a much better match for the X-T5 pixel density than the older kit lens architecture. One small detail that really matters is how the newer stepping motors handle the AF micro-adjustments on the 40MP body. It feels way more precise than those older motors. Youll get much cleaner results in the Alps without that mushy look, and it wont break the bank like the heavy native options.

Coming back to this an hour later... honestly its such a letdown how that 40MP sensor reveals every little flaw in the older glass. I have had issues with several lenses that were sharp on my older bodies but just look mushy now. Its frustrating when you spend that much on a new camera and the kit glass lets you down right before a big trip. The actual best all-arounder for you really depends on two things for a place like Switzerland:

• Are you mostly shooting wide vistas, or do you need that extra reach to punch in on mountain peaks?
• How much do you care about low light performance for indoor or evening shots? That 18-55mm is definitely showing its age on the X-T5. I really wanted it to work too, but the resolution just isnt there anymore. Let me know about those priorities and I can help you pick something that actually resolves that high res sensor properly.

^ This. Also, I have to respectfully disagree with some of the advice suggesting those ultra-light third-party zooms for a trip like this. In my experience, when you are heading into the Swiss Alps, the mechanical reliability of your kit is just as critical as the optical resolving power. I have tried many different setups over the years, and I once had a lens mount from a budget-friendly brand basically seize up in sub-zero temps because the thermal expansion coefficients of the materials didnt match the camera body. When you are shooting on a 40MP sensor, any tiny alignment issue from a less-than-sturdy build gets magnified. If the glass isnt perfectly centered within the barrel, one side of your mountain landscape is gonna look soft regardless of the aperture. Plus, when you are dealing with freezing wind and snow, weather sealing is actual insurance.

• The technical data shows that high-res sensors require much tighter tolerances in the internal lens construction to maintain sharpness edge-to-edge.
• I found that the one I got for my last mountain trek handled the high altitude pressure changes way better than the cheaper plastic alternatives.
• Communication protocols between the glass and the body are vital for that IBIS to hit its rated stops. Honestly, dont just look at the aperture or the price tag. Focus on the build. You dont want a mushy image just because the lens elements were shifting slightly in the cold or the stabilization was fighting the body.