To open the Wikipedia app, you either have to search for it, or you have its icon in a convenient spot.
With my solution, neither is necessary. A simple "!w" in the Safari search bar means "run this search in Wikipedia". If all you ever want to search is Wikipedia, then fine, my solution isn't very useful, but DuckDuckGo has tens of thousands of other bangs. !a will search Amazon, !py will search Python documentation, !so will search StackOverflow, !i will search Google Images, and so on. And you can make suggestions for more - in my experience, they add new bangs that users suggest in under 6 hours.
All of that is accessible from just the Safari icon on your homesceen.