The main benefit is that you end-up with no merge conflicts in semi-opaque files.
Though I think you're still stuck with xcode ? can you use a CLI toolchain (directly calling clang and so on) to compile, build and sign an IPA ? from the little I've seen of Xcode, it sucks (a lot): random crashes, GUI & behaviour inconsistencies, bad file management, etc...
FWIW, Apple has never required storyboard. You can do everything in code if you -really- want to do it that way, no problem. Personally, I like offloading a lot of the visual stuff to storyboard/xibs unless you start getting crazy with custom animations and so forth.
There is a third party IDE: AppCode by jetbrains which does most of what you need (and apparently lots of things better than Xcode) but i've never used it for any long periods
Xcode gets a bad rap, but i use it every day and can't remember the last time the current version crashed or did something strange, maybe i'm just used to it by now though
For iOS, however, it seems you're indeed kinda screwed - you have to go through Xcode and the atrocious storyboards stuff.