I don't think this version of Namor would be a effective swimmer. I also don't think that build type fits the character. Swimmers builds are more streamline and are harder to put on that kind of muscle just due to the nature of the sport.
French Olympic Swim Team
American Olympic Swim Team
As you can see here even the more boxier guys on the American Olympic swim team still have a more stream line physique.
But again that is just how I feel.