Just saying. Every one of those things you listed, my mother thinks is an advantage, not a drawback.
proprietary interface - she knows that to get something that really works, she just goes to the Apple store. There's never any "driver" or compatibility issues. She gets a straight answer from someone she trusts.
designed to sync through itunes only. Yep. She loves that. Nice and simple, and again, one easy path to getting what she wants.
she doesn't use Outlook or Google apps (whe wouldn't know a google app if it came up and introduced itself). She doesn't want complexity layered on top of her nice simple interface just to make someone else's life easier.
excessive control over apps - well "excessive" is a judgemental term, but she's happy there's next-to-no malicious apps for the iPhone compared to other vendors offerings. She knows she's not that technical, and she likes that the people who do know techy stuff are helping her against these malicious apps.
clumsy UI - well, simple anyway. Simple is good. Simple is easy to understand, and she likes easy to understand.
I'd be willing to bet there are more people in this world who are on a technical level with my mother, than with you or I; which is why Apple have maintained these "drawbacks" - because they're advantages.