One thing should be mentioned, something that I noticed in Celestia's dialogue right before she sang. She mentioned Twilight making friends as being part of her "test." It could be nothing, but it kind of leaves the impression that Celestia truly doesn't care about the rest of the Mane6, and only is/was using them in order to solely beniefit Twilight in reaching Celestia's goal for her.
But maybe I'm just being a little pessimistic. Though your "stepping stones" analogy would actually work, if this were true. ( Which of course I hope it is not.)
One thing should be mentioned, something that I noticed in Celestia's dialogue right before she sang. She mentioned Twilight making friends as being part of her "test." It could be nothing, but it kind of leaves the impression that Celestia truly doesn't care about the rest of the Mane6, and only is/was using them in order to solely beniefit Twilight in reaching Celestia's goal for her. But maybe I'm just being a little pessimistic. Though your "stepping stones" analogy would actually work, if this were true. ( Which of course I hope it is not.)