Great thread. I think Konzy is the one who nailed it. Having a lens that will get you the shot in most conditions quickly and reliably is often more important than absolute IQ. The 18-135 is a great lens when you aren't focused primarily on photography but want the ability to capture that special scene or moment. It focuses quickly and is nicely weather resistant. When I traveled with my late wife I couldn't concentrate first on photography the way I do when I go out on my own. She was reasonably tolerant of my photo obsession but the travel together was about, well, travel together. Record photos were nice. The occasional magic moment was easy to capture with the "swiss army knife" lens. And domestic tranquility was ensured. Consider the extra lens cheaper, and less painful, than couples counseling.
As Fuji owners we can get carried away with having the best lenses. But, corner to corner sharpness is really not that essential to most non-landscape or architectural photos. Getting the shot usually is the primary goal. Good photographers work with the limitations of their equipment, whatever that is, and get good photos. Period. Just look at any famous travel photographer. Many, many of photography's iconic shots are not sharp, sometimes not totally in focus. The photographer's eye is the crucial element.
Besides, having to change lenses because you have the wrong focal length on the camera has cost all of us once in a lifetime shots. If it hasn't, you aren't looking for time sensitive photos. Remember the old documentary photographer adage, f/8 and be there.
My last trip with my wife I took the 18-135, the 35 f1.4 and the Samyang 12. One do everything lens. One fast interior lens for frescos and one low light normal lens. No regrets. I do own the 55-200. I use it. I like it.
If I could offer Sapphire one piece of advice it would be sell all her old Canon gear and still get the 18-138. Using two systems seldom serves anyone. Muscle memory gets mixed up switching cameras and it's just extra weight to schlep around.