1. What is the weight of Winnebago View and Fleetwood icon/pulse
It depends on the year and model, but the View & Navion usually have a higher OCCC, which translates into lower unloaded weight.
2. Is there difference in mileage (like a 1-2mpg difference)
I'd guess that there's no difference in mpg.
3. Build quality
Loaded question, but here's an opinion from a mechanical engineer's perspective. I've owned a Fleetwood, but it was a 93, so it's not a fair comparison, but build quality back then was just fair.
The View & Navion have a full aluminum sheet under the coach floor, interlocking floor, walls and roof and large aluminum extrusions in the front corners of the coach to help stiffen the structure. For me, this is much more important than anything inside the coach. I can replace stuff that's inside, but the coach body has to be well designed to withstand the rigors of many years and miles.
I looked at the normally hidden things inside an Icon and saw wiring, plumbing and heating ducts seemingly assembled in a very haphazard manner. It didn't give me much confidence in the rest of the coach, but I only had a short time to inspect it. That doesn't mean that it won't function correctly, just that I prefer to see better arrangement of these items.
Obviously, owners of most brands of motorhomes are going to favor what they own or they would have purchased the competition, so my suggestion is to enjoy what you have and forget about the other brands.
Ignoring the resale value (which obviously Winnebago tops)
Personally, I feel the build quality of Icon/Pulse is significantly better than that of View
