I'm a few weeks off from completing my performance evaluation between Swift and React Native in an iOS environment, It's my exam project to graduate from university. Tackling this project from a web developer perspective was a bit of a challenge when I wanted to learn and understand how to develop iOS applications "the right way". Overall I found Swift to be a fairly "easy" language to get a grasp on, the big problem for me was the cocoa touch framework which was a real pain to get it to function properly. Overall it went a lot quicker for me to create the same design and functionality in the React Native artifact but this is also heavily influenced because I usually work with the React.js framework when building web projects. If you're okay with being locked into the Apple ecosystem since you pretty much only create MacOS, iOS & watchOS applications in Xcode then I would say that Swift is an excellent​ language to get into. If you wanna touch something "wider" then I would personally​ look into Go for microservices or maybe Python/R for machine learning depending on what you wanna create. Also,​ it's worth mentioning that you can now create ML and AR applications in Xcode utilizing the specific framework combined with Swift. Best of luck mate! :)