Earlier quoted context omitted.
The Lightning connector being proprietary does suck, but it's far and away the best mobile device connector I've used. It's small, easy to connect, and disconnects fairly easily on tug. USB-C is pretty nice, but for similar feature set you have a much larger connector.
Lightning and USB-C aren't really comparable because USB-C supports USB 3.1 while Lightning is limited to USB 2 speeds for everything, including video out. Which means that Apple have to compress the video out and stick an entire ARM SoC in their very expensive AV adapter to decompress it, and this degrades the picture quality. By comparison, USB-C can carry uncompressed HD video, power, and a fast USB 3 data link at…
So in terms of the connector itself, they're still pretty comparable, it's just that Apple for whatever reason didn't want to add support for it.
Edit: Cleared up some things that were actually untrue after researching it a bit more.