The key point in your first paragraph is "especially in devices with faster GPUs". The iPhone 4's GPU was barely powerful enough in the first place- Apple took a GPU that did well for a 480x320 display, added a slight amount of juice to it, and put it in a phone with a 960x640 display. That's why I mentioned the 3GS-it has a very similar GPU to the 4, as opposed to the much more powerful GPU in the 4S. Seeing as how iOS heavily utilizes the GPU on a consistent basis, that's not a good thing.
I somewhat agree with your next point. Except, I don't think Apple intentionally wrote unoptimized code, they simply didn't have enough time to optimize it before the public release of iOS 7. That's probably why iOS 7.1 runs much better on the iPhone 4. Given a little more time, Apple was able to make the necessary changes to make it run smoother.
Mate, you are not going to win this ...
They are convinced Apple is ruining their customer satisfaction ON PURPOSE ... Yes a very good way to gain customer fidelity
Sunking101 is spreading fud on iOS 7 in almost every post lately.