You have an interesting take on what is considered designed well and what isn't. With that in mind...
Did it ever occur to you to read the owners manual (you can download it through iBooks) for your several hundred dollar device? I'm going to guess no. Because not only did Apple account for this type of mistake, it made recovering from it very simple. So for future reference, when you fat finger the delete button on a section of selected text and you need it back here is what you do.
1) Shake iPhone.
2) Tape undo.
Yes, it is that simple, when you are doing real time editing, to undo a mistake that is made.
So the issue isn't a poorly designed product. It is a mater of you simply not learning to use your device properly to begin with.