The point I think most people should consider instead, is that building an app is not the same thing as building a business. Building the app is comparably easy, once you've proven that you understand the market, your target buyer, and have a unique insight/tool/solution to offer that you can deliver via software.
If you want to learn a technology, by all means build an app. But if you want to build a SaaS business, keep focused on building the _business_. The app, it turns out, is the easy part.