When you've been doing aikido for a while you can see who is good and who is not, and what they are good at. However beginners are not aware of this - ranking (and the restriction of hakama use) I think is useful to say, I think what this person has to say about aikido has some validity.
Also, like it or not, grading helps to encourage people to progress; it enables students to focus on certain aspects. In addition, although we all do the same techniques, there are some techniques I consider absolutely fundamental to aikido (e.g. ikkyo, irimi-nage), whilst others are useful but less flexible in their application (e.g. aiki-otoshi).
I think we need to formulate aikido initially, and once the individual techniques are there we can break them down and become more fluid. Starting by saying, 'there are no techniques, just blend' would result in slow progression and many injuries.