Nice Article. We at Digicorp help startups build usable products. Product Managers are the ones driving these products. I completely agree that writing is the most important skill.
I am practicing writing since last few months and it forced me to be clear in my thoughts. According to me this is most important for anyone who wants to gain more out of life.
A Product Manager having clear vision about the product, its priority and expectation of team will increase his chances of building a successful product.