And it gets better. Don't like apple's calendar app? On any other device, you could just get a better calendar app. One that does what you want. But not on an iOS device. Apple don't allow that - it's "duplicating apple functionality", and they won't let you put an app that does that on their store. And they won't let you sell it or even give it away via any other channels either. And it doesn't matter that it's doing things the inbuilt calendar app can't even dream of - it's a calendar, ergo you can't do that.
This is the reason I will never buy an iOS product. If I buy a computing device, I want to choose what I install on it, and from where. And if I don't like some default app for something, I want to be able to get an alternative.