New member here, had my X-T1 etc for 18 months now and loving it.
I recently bought the 16-55, and I was very unsure at first. I was travelling in Japan and managed to pick it up for £440 (compared to ~£1k new / £700 used) here in the UK) and so bought it mainly as an experiment, since I could always sell it on.
Its a lot bigger and heavier than the 18-55, but for me, I think its worth it for the following reasons:
1) although the 18-55 is 2.8-4, even at 23mm or so, its getting close to 3.5, so for most of the 'normal' range, this lens is significantly faster.
2) I love the wide end, and the 2mm extra is quite a lot at that end.
3) At the portrait end, the bokeh is lovely. Its enough to keep me away from the 56 1.2 for the time being.
4) the weather sealing is useful, and means that walking around I just don't worry about the camera. The side benefit of WR is that is must better sealed against dust etc... which is a good thing too.
So for me, I accept the weight compromise, and its still a whole lot smaller than the equivalent DSLR setup.
I love the primes, but I bought it because I love to take pictures of my 1yo son, and the primes mean't i often missed a cool shot because I didn't have the right lens on the body (any of you with kids know they ain't gonna sit still for anything!). With this lens, I pretty much get everything.
I'll hang on to the 35 1.4 as my go everywhere small prime for street/portrait/landscape etc... and might grab the 27mm just so i can pocket the camera when necessary.
Now I just need to figure out an ultrawide, but thats for another topic....