There is always a learning curve with anything new and yes very simple apps are easy to write. Usually, when you get into a project the project scope starts to expand. For example, when writing a simple app to convert temperature from Celcius to Farenheight you might want to start saving the history in a database, maybe link the temperature reading to a customer or device and then move the data back to your own internal systems back at the office etc. That's when a whole wave of technology and languages hit and the required knowledge curve can go exponential.
Uploading your business app to the apple store is, arguably, not straight forward and Apple could possibly streamline the process a little.
Apple set a very high standard for apps, ( which is a good thing ). Apps have to be somewhat unique in function and name, technically elegant, have a good measure of artistic design and finally pass through some 200+ tests and conditions before Apple will approve the app for release. Our first app, for example, took 4 submissions and 5 weeks before being approved. Not because of any bugs or design issues but the standards required for a commercial app and the data storage size invoked new rules that we were not aware of then. However, our last app of 16,000 lines of code was approved in 2 days. It's all a learning curve.
So if your app is reasonably simple and you have a long run of focused time ahead of you, go for it.Often it's easier and cheaper in the long run, to let someone write it for you while you focus on your core business.