It is often argued that weak consistency models impose an extra burden for programmers. To what extent is this statement actually true?

Use object-oriented design where it makes sense to. Structured design is a viable option in some situations. Just why is this happening, etc.

To what extent are proofs of concept different from prototypes?

Perhaps it makes sense to investigate the wide variety of programming methods at our disposal. How can we account for the presence of so many competing paradigms? You are not free to choose otherwise. Your own words would help me understand it much better.