A better metaphor, I think, would be an orchestra. Each one has their independent skill, but the goal is not a display of that, but of creating a symphony out of the various instruments, playing low or not playing or playing at the right time, syncing with the notes. People with perfect independent skills as displayed in a solo performance, can still mess up the harmony if they are out there to perform, instead of "perform a part". Each member doesn't have to pick up the skill in the other instrument, but bring whatever he is good at (which may not be many, but just that one thing) and play the part that fits in the piece. This can be seen better in orchestra practice in learners, where they play even their part imperfectly, but over a period of time, improve their ability to play their part well.
Its not like we "must not" develop independent skills, it's that such skills should subserve the cause of happiness and harmony, even if with occasional small spikes. In relationships, it's okay to be unskilled yet happy, and worse to be skilled yet unhappy. As to who should adapt, all of them. If it's two of them, both. One on Issue A today, another on Issue B tomorrow. If someone can't develop a certain skill independently, that should be fine, because we are in a relationship, not in a training institute or talent exam.
As to the oar metaphor, it would depend whether we are working for (1) a "best rower" award or (2) reaching a destination or (3) the fun of rowing together or (4) acquiring the skill better to prepare for a whirl ahead. 3 and 4 relate better to relationships success and use the skill for a better experience of being together. 3 will won't even expect a good skill from the other, just to row a bit here and relax a bit there. 1 and 2, however, are about "urging" the other to become something or "requiring" them to build a skill, which may or may not be their cup of tea. Excellence is not a good objective for relationships, happiness is. We can be imperfect, dependent, unskilled in one area, be independent and skilled in another, and yet be happy with someone who is the converse.
As to the book, I believe and endorse that view, have found it to be true in my experience and therefore find nothing wrong in quoting a source of inspiration, where applicable. It has got nothing to do with independent thinking. It's good to use some library in our lives and test them in practice. It's not much different from quoting a book cover.