From the RPi foundation's mission statement:
"But we felt that we could try to do something about the situation where computers had become so expensive and arcane that programming experimentation on them had to be forbidden by parents; and to find a platform that, like those old home computers, could boot into a programming environment. "
The point of the thing is to be a cheap platform for learning programming and principles of Computer Science. They go on to say that the multimedia capabilities were added to make it interesting to kids that weren't interested in a purely programming oriented device. I have to think the GPIO capability is basically for the same reason, although they don't mention it explicitly. I believe the charter was expanded at some point to include third-world students.
*ALL* the RPis require a power supply, SD card, cables, mouse, keyboard, etc. The only thing the Zero really lacks compared to (some of) the other versions is Ethernet and multiple USB ports. AND ITS $5.
The fact that the Pis have become attractive to hackers doesn't make your needs paramount. If you're using them for embedded system development and it's such a pain in the ass to move cables around, you have enough money- if you don't already have most of the crap in your closet- to buy two complete setups. (I do, with 2-3 each of the various versions of Pi). It's not that expensive.
RPis absolutely fulfill their intended purpose, even if the single core models are a little pokey. While pushing things beyond their envelope is admirable and What We Do, you can't really complain if things get a little sketchy outside of expected operational modes.