I am a believer that your messaging/positioning has to be consistent with how differentiated your product really is. Customers will quickly figure out what is marketing fluff vs. product truth anyway! So - even if your product is not the market leader but your research tells you that you have a killer product - i'd suggest being aggressive with the messaging and positioning and taking the fight to the competition! On the other hand - if you are entering a new segment with a 'v1' version of a product that you know is not very competitive yet, i'd lean a bit more towards reflecting the vision of the product/strategy vs. capabilities of the product itself in the messaging/positioning.