Sorry but what ? Apple has one of the best concurrency implementations on ANY platform. GCD is superbly designed and combined with blocks makes concurrency trivial.
The biggest problem is that developers often try and over optimise.
> which I have timed to usually clock in at 8-9 seconds, but which can take as long as 20 seconds
This is definitely not normal.
> iOS software is fucking slow.
No. It really isn't.
> This is definitely not normal.
Big consolation to users experiencing this! That's a Linux-level response to user concerns.
Then we are observing very different realities. Beginner's mistakes have been evident for years and years in the iTunes (desktop) application where the GUI thread is routinely blocked by anything from network activity to slow disk IO.
With the latest generation of iOS, these problems have started cropping up elsewhere in iOS apps. For instance if you use the podcast app as intended, and download content directly on your iPhone, the UI has a tendency to block on IO operations that should have taken place in the background. The UI will hang and refuse to scroll. Also, the player has become really temperamental -- often refusing to accept volume control inputs via the screen for many seconds after laboriously starting to play a stream.
(And why the hell did Apple have to split up the iPod application in the first place. Now you have iTunes U, which is sluggish and buggy, you have Podcasts, which is sluggish and buggy etc. WHY!?)
I don't know if it was because I was running out of disk space, but taking photos and texting became absolutely terrible on my iPhone 4. iOS 6 made it even slower.
If there are substantial Notes? Good night. Supercomputers brought to their knees.