But let me start by saying that if you are an umbrella user and you like them, you don't need my opinion.
On the PCT many people start out with umbrellas. Many find that when they want them for shade in the hot, open country of the desert, the wind can make them unusable. When they want them in the cold rain of Washington, they need rain gear anyway to keep wet vegetation from soaking them. For me, that makes umbrellas too specialized.
In my experience I tend to see many more umbrellas at the start of long trails than at the end.
My rain gear is multi purpose.
2. Wind block
4. To wear whilst doing laundry
When I REALLY want and need rain gear is when it's wet, cold and windy. Conventional rain gear is much better under those conditions. Personally, I'm not going to carry both a rain parka and an umbrella, so a rain jacket (plus rain pants depending on where and when) wins easily. I leave unneeded gear at home, and for me that includes an umbrella every time.