I have used both and honestly, I am super satisfied with the Tamron 18-300mm f/3.5-6.3 Di III-A VC VXD for travel. The Fujifilm XF 18-135mm f/3.5-5.6 R LM OIS WR is decent but feels a bit old on that 40mp sensor. The Tamron works well for everything from wide temples to distant street scenes. It is a tad heavy, but having that range in one lens is just so easy.

Jumping in here, you really gotta be careful with that 40MP sensor because the pixel density is pretty unforgiving on older glass. I would suggest looking at the Fujifilm XF 18-120mm f/4 PZ LM WR instead. Honestly, it handles the high resolution way better than those older zooms.

• Constant f/4 aperture prevents annoying exposure shifts while zooming
• Internal zooming keeps the dust out during travel
• Usually fits perfectly under your 800 budget

^ This. Also, honestly, I had a pretty rough time with that older 18-135 when I took it to Kyoto a while back. Not sure if it was just my copy, but the corner softness was actually pretty depressing once I got the files on a big screen. It kinda ruined some of my favorite temple shots tbh. IIRC, some people said those older designs just cant keep up with the 40mp sensor on your X-T5, which makes things look way mushier than they should. The superzoom range sounds great but it’s a lot of weight to carry for two weeks if you end up disappointed with the results... I think a smaller zoom plus a prime might be better even if it isnt strictly all-in-one. It just feels risky spending that much money on something that might not do the sensor justice. Just curious tho, what are you actually planning to shoot most? Like, are you doing mostly street scenes or wide landscapes?