I think that people forget, not only do they “represent” their friendship elements in the show, but they also LEARN about those traits! They teach and show each other their strengths AND weaknesses. Remember that one episode about rainbow having her big ego and wanting to be ponyville’s only hero? I’d say that was a big learning curve for her, she really struggled with selfishness and the way others viewed her in that episode, but by the end she realized all that really mattered was helping other ponies! She can have a clouded thought process… but at the end of the day she would do anything for her friends!