Indeed - I've hiked almost 3k miles carrying an umbrella. Worn rain gear is a compromise between breathability and waterproofness - even if you keep the rain out, you'll sweat and it's trapped inside. Umbrellas keep rain off you, are very breathable, and double as sun protection when it's really hot. Only downside is when it's windy and rainy, so it's nice to have a poncho too.